Lidar system with polygon mirror

ABSTRACT

A lidar system includes one or more light sources configured to generate a first beam of light and a second beam of light, a scanner configured to scan the first and second beams of light across a field of regard of the lidar system, and a receiver configured to detect the first beam of light and the second beam of light scattered by one or more remote targets. The scanner includes a rotatable polygon mirror that includes multiple reflective surfaces angularly offset from one another along a periphery of the polygon mirror, the reflective surfaces configured to reflect the first and second beams of light to produce a series of scan lines as the polygon mirror rotates. The scanner also includes a pivotable scan mirror configured to (i) reflect the first and second beams of light and (ii) pivot to distribute the scan lines across the field of regard.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/965,519, filed on Apr. 27, 2018, entitled “Manufacturing a BalancedPolygon Mirror,” which claims priority to U.S. Provisional PatentApplication No. 62/590,235, filed Nov. 22, 2017, entitled “Low ProfileLidar Scanner with Polygon Mirror,” the entirety of which isincorporated herein by reference.

FIELD OF TECHNOLOGY

This disclosure relates generally to lidar sensor heads and, morespecifically, to multi-mirror lidar sensor heads having a compactconstruction so as to occupy minimal area when deployed on a vehicle.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Light detection and ranging (lidar) is a technology that can be used tomeasure distances to remote targets. Typically, a lidar system includesa light source and an optical receiver. The light source can be, forexample, a laser which emits light having a particular operatingwavelength. The operating wavelength of a lidar system may lie, forexample, in the infrared, visible, or ultraviolet portions of theelectromagnetic spectrum. The light source emits light toward a targetwhich then scatters the light. Some of the scattered light is receivedback at the receiver. The system determines the distance to the targetbased on one or more characteristics associated with the returned light.For example, the system may determine the distance to the target basedon the time of flight of a returned light pulse.

While the precision and efficacy of lidar scanners have continuallyimproved, the power requirements, heat dissipation, and physicaldimensions of existing lidar scanners have posed obstacles to designersof lidar systems. With the increasing prevalence of the use of lidarsystems in vehicles, such considerations are of increased concern todesigners of lidar systems.

SUMMARY

A lidar system including a light emitting light source (i.e., a laser),a scanner configured to direct the embedded light to scan a field ofregard (FOR) of the lidar system in accordance with a scan pattern, areceiver that detects light scattered by one or more remote targets, anda controller to control one or more mirrors of the scanner, is provided.The scanner includes both a polygon mirror and a planar mirror. Thepolygon mirror may be in the form of a rotatable block having a firstwall, a second wall spaced away from and parallel to the first wall, anda plurality of reflective surfaces extending between the first andsecond walls, the reflective surfaces being angularly offset from oneanother along a periphery of the block. The planar mirror rotates aboutan axis orthogonal to an axis of rotation of the polygon mirror, and isthereby considered a pivotable oscillating planar mirror. At least thescanner and the receiver may be disposed inside a housing of a lidarsensor unit (or “sensor head”), and the lidar system can include one orseveral lidar sensor units.

The polygon mirror may also be provided with a motor to power itsrotation that is disposed at least partially, but preferablysubstantially or entirely, within the rotatable block. By arranging themotor for the polygon mirror within the rotatable block of the polygonmirror, the overall three dimensional footprint of the scanner can befurther reduced.

The polygon mirror may be provided with one or more tabs that passthrough a stationary photo-interrupter as the polygon mirror rotates.The photo-interrupter provides feedback data indicative of therotational speed of the polygon mirror, which feedback data can then beprocessed by a controller associated with the motor of the polygonmirror to regulate, stabilize, or adjust the rotational speed of thepolygon mirror as needed.

The scanner of the lidar sensor unit is provided with a low profile whencompared to conventional multi-mirror lidar systems. Certain structuraland operational features of the lidar sensor units of the presentdisclosure may be employed, individually or collectively, to not onlyminimize the three-dimensional footprint or volume of space occupied bythe lidar scanner, but also serve to improve aerodynamic performance(both internally and externally), reduce audible noise, reduce heat, andimprove resistance to vibration, acceleration, deceleration, or otherenvironmental factors that might otherwise negatively affect scanneraccuracy and performance.

The orientation of the scanner, and specifically, the orientation of theaxis of rotation of the polygon mirror, may be selected so as to alignwith an orientation of a vehicle in which the lidar sensor unitoperates. In some implementations, however, a lidar system operating ina vehicle includes multiple lidar sensor units, with at least some ofthe lidar sensor units oriented differently from each other.

The planar mirror of the scanner may be provided with an optimizedgeometry to enhance durability and service life. For instance, theplanar mirror may have a center of gravity closer to its reflectivesurface than conventional planar mirrors of lidar scanners. This may beeffected by constructing a pivotable backing or support surface for thereflective surface of the planar mirror of a honeycomb structure orother ribbed structure, with material arranged such that the center ofgravity of the planar mirror is closer to the reflective surface than toan edge of the ribbed or honeycomb structure opposite the reflectivesurface.

The speed of oscillation of the planar mirror may be controlled so as todynamically vary distances between scan lines. In general, a scan linecan have a horizontal orientation, vertical orientation, or any othersuitable orientation. In at least some of the embodiments discussedherein, each scan line corresponds to a reflection of the emitted lightfrom one of the reflective surfaces of the rotating polygon mirror. Thedistances between scan lines can vary on a frame-by-frame basis, and canvary in different portions of the field of regard. A drive signal of amotor driving the speed of oscillation of the planar mirror can beshaped as a Gaussian to optimally space scan lines apart. For example,the Y-scan mirror can be driven with a Gaussian-type function so thatthe mirror has a relatively high scan speed at the ends of its motionand a relatively low scan speed near the middle of its motion. This typeof Gaussian scan produces a higher density of scan lines near the middleregion of the FOR and a lower density of scan lines at the upper andlower ends of the FOR.

The width of the planar mirror can determine the horizontal scan range,also referred to below as the horizontal dimension of the field ofregard (FOR_(H)). For a given polygon mirror, FOR_(H) can be increasedby selecting a wider planar mirror. The lidar sensor unit can supportmodular optical assembly, so that planar mirrors of different widths canbe compatible with the same remaining opto-mechanics of the lidar sensorunit. Thus, by providing an oscillating planar mirror of a significantlygreater width than the reflective surfaces of the rotating polygonmirror, not only can the oscillating planar mirror achieve desired fieldof regard along the vertical dimension (FOR_(V)), but the oscillatingplanar mirror, in concert with the polygon mirror, can alsoadvantageously increase the FOR_(H), all while reducing the overallthree dimensional footprint of the lidar sensor unit.

The planar mirror preferably has a range of motion that exceeds thevertical dimension of the FOR. For instance, if the FOR is 30°vertically by 120° horizontally, the range of motion for the planarmirror (which, for the sake of convenience, is also referred to hereinas a Y-scan mirror) can be 60° vertically, to accommodate a 30° verticalcomponent of the FOR in various ranges. This enables a lidar sensor headto scan a greater range of vertical area, such as when a vehicle onwhich the lidar sensor is mounted approaches an incline.

As explained in more detail in the following detailed description, thepolygon mirror, at any given time during its rotation, includes at leasttwo active, adjacent reflective surfaces. This enables the lidar sensorunit to direct pulses toward different sections of a scan line so as toprocess at least two distinct return pulses within the time of a singleranging event. The outbound pulses can scatter from the same remotetarget or different remote targets. Using two beams of light with twofacets of the polygon mirror thus increases the FOR_(H) of the lidarsensor unit without increasing the time it takes to scan one line.

The adjacent reflective surfaces direct the output beams towarddifferent portions of the planar mirror. Thus, the lidar sensor unit canhave two active “eyes” that share both the polygon mirror and the planarmirror, thereby providing both a cost reduction and a size reduction.The beams are incident on the respective surfaces in such a manner thatprovides a large angular separation between the outbound beams, so as toreduce the probability of cross-talk detection. In one example, twobeams can be offset along the x-axis by half a pixel to produce twotimes the pixel density in the overlap region (e.g., for a pair ofadjacent pixels generated using one beam, another pixel centered at themidpoint between the pair of pixels can be generated using the otherbeam). In another example, two beams can be offset along the y-axis byhalf a line to produce two times the pixel density in the overlap region(e.g., for a pair of adjacent scan lines generated using one beam,another scan line centered between the pair of adjacent scan lines canbe generated using the other beam). The first approach involvesoffsetting the pixels along the x-axis so that, in the overlap region,the pixels from one beam are interleaved along the x-axis with pixelsfrom the other beam. The second approach involves offsetting the scanlines along the y-axis so that the scan lines are interleaved in theoverlap region. These two approaches (interleaving pixels andinterleaving scan lines) are independent of each other and can beimplemented separately or together.

By having two adjacent active surfaces, and at least two inactivesurfaces of the rotating polygon mirror at any one time, a baffle orshroud can be provided around the inactive surfaces so as to furtherreduce aerodynamic drag and aid in air circulation of the polygonmirror. The use of such a baffle or shroud is not possible with a 360°scanner, as such a shroud would block active reflective surfaces of themirror.

Input and output beams can be incident on the same mirror operating in alidar scanner, or the same multi-mirror assembly including a mirror togenerate scan lines (e.g., a polygon mirror) and another mirror todistribute these scan lines along the other dimension (e.g., a planarmirror). The fields of view (FOVs) of the beams can be arranged tominimize the overall surface area. In another aspect of the presentdisclosure, the fields of view of two output beams define relativelysmall circles, whereas the field of view of the input beams defines arelatively large circle. The smaller circles are arranged adjacent tothe larger circle, with little or no overlap, and with the imaginaryline segment connecting the centers of the smaller circles displacedrelative to the diameter of the larger circle. This more compactarrangement facilitates minimization of the overall three dimensionalfootprint of the scanner.

The lidar scanner of the present disclosure preferably employs a singlelens with off-axis illumination for two detectors, which are placed inthe same optical path. The displacement of the transit beam relative tothe center of the lens allows the detectors to be placed adjacent oneanother and off-center, thereby further facilitating a minimized overallprofile. The detector diameter is approximately 50-150 microns, and thedetector separation distance is approximately 0.5-2 mm.

The use of off-axis illumination eliminates the need to use an overlapmirror with a center hole, which sometimes is referred to as a “doughnutmirror.” In particular, the beams are coupled into the scanner by theside of an overlap mirror that reflects input light to the detector. Theoutput beam(s) and the input beam(s) thus are not entirely coaxial, asdiscussed in more detail below. The output beam(s) and the input beam(s)are offset relative to each other spatially and angularly. In otherimplementations, however, a doughnut mirror can be used with the polygonmirror and the planar mirror of this disclosure.

Methods of manufacture of a suitable polygon mirror are also disclosedherein. To obtain optimal balance of the polygon mirror, and ensure thefield of regard is accurately scanned, high-energy laser pulses are usedto remove matter at precise locations of the rotating polygon mirror.This can be combined with initial drilling for coarse balancing (so asto achieve both coarse and fine balancing). More particularly, a coarsebalancing procedure using a drill or another suitable equipment can beused to form a relatively well-balanced block, and the surfaces can bemade reflective (as explained in greater detail below). The block thencan be mated to a motor in an assembly to be used in a scanner (ratherthan using an assembly specifically set up for manufacturing ortesting). Once mated to the motor, the block can be rotated, andhigh-energy laser pulses can remove excess material from the block toachieve a high degree of balancing.

The polygon mirror is preferably manufactured by surface replication. Inembodiments where the polygon mirror includes an even number of facets,pairs of opposite facets may be serviced simultaneously. While afour-sided polygon mirror will be disclosed as the preferred embodiment,the specification will explain that other numbers of sides are possible,with the understanding that the more facets of the polygon mirror, thecloser the overall polygon mirror resembles a circle.

The lidar scanner can be implemented in a manner that directs twoangularly separated pulses toward different sections of the scan lineand processes the return pulses within the time of a single rangingevent, where the two pulses reflect from the same reflective surface ofthe polygon mirror. Thus, according to some implementations, a singlesensor head includes a total of four beams and four detectors: each pairof beams includes two angularly separated beams that reflect from thesame surface of the polygon mirror. The lidar system can process returnpulses corresponding to a non-integer separation in pixels (for example,an angular separation corresponding to 5½ or 11½ pixels). In thismanner, the system can superimpose the return values to more accuratelydetermine the values of pixels 1, 2, 3, . . . , N of the scan line.Otherwise, the lidar system receives duplicate readings for many of thepixels. Additionally, separating the two beams by a significant numberof pixels (e.g., approximately 9-13 pixels rather than 3-5 pixels)mitigates problems with defocusing of the beam received at thedetectors. The separation distance between the detectors (e.g., 0.8-1.2mm) corresponds to the angular separation of the beams (e.g., 2-3degrees). Since the two detectors are separated by a certain distance,if the beams become defocused, there will not be a problem withcross-talk where light from one beam spills over to the other detector.

Alternately, the beams are interleaved/offset by ½-pixel so that onebeam provides information about pixels 1, 2, 3, etc., and the other beamprovides information about pixels 1½, 2½, 3½, etc. Since the pixels canbe numbered in any fashion, this can also be expressed as the beamsbeing offset by 1 pixel (e.g., one beam samples the odd pixels and theother beam samples the even pixels), where adjacent pixels may have someamount of overlap.

In some implementations, diffractive optical elements (DOEs) can be usedto produce angularly separated beams. In other implementations, however,the lidar system uses fiber-optic power splitters and mechanicalpositioning/aiming to produce the angularly separated beams. Forexample, the output from the light source is split four ways (e.g., witha 4×1 power splitter, or with 3 2×1 power splitters) into fourfiber-optic cables. Then, each of the four fiber-optic cables isterminated by a collimator (essentially, a lens that is rigidly coupledto the end of a fiber) to form a collimated free-space output beam. Foreach “eye” of the sensor head, two collimators can be positioned andaimed to form two angularly offset output beams (e.g., with a 2-degreeangle between the beams). These two beams are directed so that togetherthey reflect off of one face at a time of the rotating polygon mirror.

Further, the splitters can also be fiber-optic power splitters orfree-space power splitters. The fiber-optic power splitters can beconsidered to be part of the light source or part of the opticalelements.

The low-profile lidar scanner head can be provided as a box-likeprotrusion on each corner of the roof of a vehicle, preferably at 45°relative to each of the edges. In a particularly preferred embodiment,the lidar scanner head may be partially embedded in the vehicle roof orother vehicle body part so only a window of the unit protrudesprominently from the roof (or hood, side mirror, rear-view mirror,windshield, bumper, grill, or other body part surface in which the lidarscanner head is disposed).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a lidar sensor unit of the presentdisclosure;

FIG. 2 is a top, front perspective view of the lidar sensor unit of FIG.1;

FIG. 3 is a front perspective view of the lidar sensor unit of FIG. 1,with the housing removed for clarity;

FIG. 4 is a right, rear perspective view of the lidar sensor unit ofFIG. 1;

FIG. 5 is a right, front perspective view of the lidar sensor unit ofFIG. 1;

FIG. 6 is a right, front perspective view of a polygon mirror and motorassembly of the lidar sensor unit of FIG. 1;

FIG. 7 is a rear perspective view of the polygon mirror and motorassembly of the lidar sensor unit of FIG. 1;

FIG. 8 is a left rear perspective view of the polygon mirror and motorassembly of the lidar sensor unit of FIG. 1;

FIG. 9 is a rear perspective view of the polygon mirror and motorassembly of the lidar sensor unit of FIG. 1;

FIG. 10 is a top perspective view of a polygon mirror of the lidarsensor unit of FIG. 1;

FIG. 11 is a rear, top perspective view of the polygon mirror of thelidar sensor unit of FIG. 1;

FIG. 12 is a right, rear perspective view of the polygon mirror of thelidar sensor unit of FIG. 1;

FIG. 13 is a rear elevation view of the polygon mirror of the lidarsensor unit of FIG. 1;

FIG. 14 is a front elevation view of the polygon mirror of the lidarsensor unit of FIG. 1;

FIG. 15 is a front perspective view of the planar mirror and motorassembly of the lidar sensor unit of FIG. 1;

FIG. 16 is a front, right perspective view of the planar mirror andmotor assembly of the lidar sensor unit of FIG. 1;

FIG. 17 is a left, front perspective view of just the polygon mirror andthe planar mirror of the lidar sensor unit of FIG. 1;

FIG. 18 is a left elevation view of just the polygon mirror and theplanar mirror of the lidar sensor unit of FIG. 1;

FIG. 19 is a front perspective view of just the polygon mirror and theplanar mirror of the lidar sensor unit of FIG. 1;

FIG. 20 is a rear perspective view of just the polygon mirror and theplanar mirror of the lidar sensor unit of FIG. 1;

FIG. 21 is a perspective view of the optical base of the lidar sensorunit of FIG. 1, enclosing a lens and a receiver;

FIG. 22 is a perspective view of several components of the lidar sensorunit of FIG. 1 in an example implementation that includes an overlap“doughnut mirror,” along with a schematic representation of examplepaths of beams;

FIG. 23 is a perspective view of several components of the lidar sensorunit of FIG. 1 in an example implementation free of an overlap doughnutmirror;

FIG. 24 is a perspective view of a path of an input beam relative to thepolygon mirror and the planar mirror of the lidar sensor unit of FIG. 1;

FIG. 25 is a perspective view of paths of an input beam and output beamsrelative to the polygon mirror and the planar mirror of the lidar sensorunit of FIG. 1;

FIG. 26A is a block diagram of an example lidar system in which thelidar sensor unit of FIG. 1 can operate in a single-eye configuration;

FIG. 26B is a block diagram of an example lidar system in which thelidar sensor unit of FIG. 1 can operate in a two-eye configuration;

FIG. 27 illustrates an example InGaAs avalanche photodiode which canoperate in the lidar system of FIG. 26A or FIG. 26B;

FIG. 28 illustrates an example photodiode coupled to a pulse-detectioncircuit, which can operate in the lidar system of FIG. 26A or 26B;

FIG. 29 is a perspective view of a housing of a lidar sensor unit, suchas the lidar sensor of FIG. 1, protruding from a surface of a vehicle;

FIG. 30 is perspective view of several components of the lidar system ofFIG. 26A or 26B, disposed on a vehicle so that the axis of rotation ofthe polygon mirror aligns with an orientation of the vehicle;

FIG. 31 is a perspective view of a roof of a vehicle, on which foursensor head unit are arranged at respective corners;

FIG. 32 illustrates an example vehicle in which one implementation ofthe lidar system of FIG. 26a or 26B can operate;

FIG. 33 illustrates an example vehicle in which another implementationof the lidar system of FIG. 26a or 26B can operate;

FIG. 34 is a flow diagram of an example method for manufacturing ahighly balanced rotatable polygon mirror that can be used in the lidarsensor unit of FIG. 1;

FIG. 35 schematically illustrates fields of view (FOVs) of a lightsource and a detector that can operate in the lidar sensor unit of FIG.1;

FIG. 36 schematically illustrates the operational vertical field ofregard FOR_(V) of the lidar sensor unit of FIG. 1 relative to theavailable FOR_(V-AVAIL) of the lidar sensor unit, within which theoperational FOR_(V) can be adjusted;

FIG. 37 schematically illustrates non-equal distribution of scan lineswithin a vertical field of regard FOR_(V) of the lidar sensor unit ofFIG. 1, in a certain operational mode of the lidar sensor unit;

FIG. 38 is a flow diagram of an example method for repositioning thevertical field of regard FOR_(V) within the available FOR_(V-AVAIL) byadjusting the oscillation of the planar mirror of the lidar sensor unitof FIG. 1;

FIGS. 39A and 39B schematically illustrate adjusting the vertical fieldof regard FOR_(V) based on detected changes in the grade of the road,which can be implemented in the lidar sensor unit of FIG. 1;

FIG. 40 is a diagram of an example detector array with two detectorsconfigured to detect return pulses associated with different respectiveoutput beams, which can be implemented in the lidar system of FIG. 26Aor 26B;

FIG. 41 illustrates an example forward scan of a pair of spaced-apartpixels based on the detector array of FIG. 40;

FIG. 42 illustrates an example interleave of scan lines in an overlapregion, which the lidar system of FIG. 26A or 26B can generate;

FIG. 43 illustrates an example scan using output beams with non-integerpixel separation, which the lidar system of FIG. 26A or 26B cangenerate; and

FIG. 44 is a flow diagram of an example method for generating pixelvalues using output beams with non-integer pixel separation.

DETAILED DESCRIPTION

A lidar sensor unit and various techniques for operating the lidarsensor unit are discussed below, in particular: (i) an example assemblyof a lidar sensor unit, and particularly a scanner of the lidar sensorunit, is discussed with reference to FIGS. 1-21; (ii) propagation oflight through the lidar sensor unit in example scenarios is consideredin connection with FIGS. 22-25; (iii) example operation of the lidarsensor unit as part of a lidar system is considered with respect to theblock diagrams of FIGS. 26A-28; (iv) example placement of a lidar sensorunit on a body of a vehicle is discussed with reference to FIGS. 29-33;(v) an example method of manufacturing a polygon mirror for use in thelidar sensor unit is discussed with reference to FIG. 34; (vi) examplemodifications to the scan pattern of the lidar sensor unit are discussedwith reference to FIGS. 35-39B; and (vii) example generating of pixelsis considered in connection with FIGS. 40-44.

I. Lidar Sensor Unit Equipped with a Scanner Having a Planar and PolygonMirrors

Referring to FIGS. 1-5, a lidar sensor unit 10 of the present disclosureincludes a scanner 11 with a rotatable polygon mirror 12 and a pivotableplanar mirror 14 that cooperates with the rotatable polygon mirror 12 toperform a scan of a field of regard (FOR) of the lidar sensor unit 10.The pivotable planar mirror 14 may be referred to herein as a Y-scanmirror, but it is understood that depending on the orientation of therotatable polygon mirror 12 and the pivotable planar mirror 14, thescanning range achieved by the pivotable mirror 14 may be in any of theX- Y- or Z-planes. The rotatable polygon mirror 12 includes a block 16having a plurality of (preferably at least four) finished reflectivesurfaces 18, 20, 22, 24. It is possible, however, to a use atriangle-shaped rotatable polygon mirror with three reflective surfaces.In another implementation, not every surface of the rotatable polygonmirror oriented toward the planar mirror 14 is reflective (e.g., therotatable polygon mirror can be a flat substrate with reflectivesurfaces on the front and back sides). More generally, the rotatablepolygon mirror 12 may have any suitable number of reflective surfaces,such as for example 2, 3, 4, 5, 6, 7, or 8 reflective surfaces. Thepolygon mirror 12 may be made from any suitable material, such as forexample, glass, plastic (e.g., polycarbonate), metal (e.g., aluminum orberyllium), metal foam, carbon fiber, ceramic, or any suitablecombination thereof.

The rotatable polygon mirror 12 further includes a first wall 26 and asecond wall 28. Each of the plurality of reflective surfaces 18, 20, 22,24 extends between the first and second walls 26, 28. The reflectivesurfaces 18-24 are angularly offset from one another along a peripheryof the block 16.

Generally speaking, as the polygon mirror 12 rotates, the scanner 11produces one scan line for each reflective surface of the polygon mirror12, and the planar mirror 14 pivots to distribute the scan lines acrossthe FOR. Thus, if the scan lines are directed horizontally, the polygonmirror 12 is responsible primarily for the horizontal dimension of thefield of regard (FOR_(H)), and the planar mirror 14 accordingly isresponsible for the vertical dimension of the field of regard (FOR_(V)).

Adjacent reflective surfaces 18-24 of the block are preferably joined toone another along a drag-reducing, non-sharp edge to promote aerodynamicefficiency and reduce audible noise. As an example, the block mayinclude rounded or chamfered edges or corners. As another example, theblock may include edges with texturing, grooves, riblets, or a sawtoothpattern.

As best illustrated in FIGS. 6-9, the rotatable polygon mirror 12 ismounted in a bracket or mount 29 on a polygon mirror axle 30, whichpolygon mirror axle 30 extends through at least one of the first andsecond walls 26, 28. A motor 32 drives the polygon mirror axle 30,thereby imparting rotational oscillation to the rotatable polygon mirror12. The motor 32 may be a synchronous brushless DC motor in drivingrelationship with the axle 30 and may be external to the block 16.Alternately, the block 16 may accommodate an internal motor, or enable amotor 32 to be at least partially embedded within the block 16, such aswhere a rotor of the motor 32 is disposed within the block 16, reducingthe overall size of the lidar sensor unit 10. The motor 32 may driverotation of the rotatable polygon mirror 12 in an open-loop orclosed-loop fashion. In general, the motor 32 can be any actuator ormechanism suitable for rotating the polygon mirror 12.

The rotatable polygon mirror 12 may additionally employ an optical beam,the presence or absence of which is detectable by a stationaryphoto-interrupter, to collect data indicative of the rotational speed ofthe rotatable polygon mirror 12. One or more tabs may be provided on theaxis of rotation of the polygon mirror 12 or an interior surface of theblock 16, which tab(s) pass through the stationary photo-interrupterduring rotation of the polygon mirror 12. Upon receiving from thephoto-interrupter feedback data indicative of the rotational speed ofthe polygon mirror 12, the feedback data can then be processed by acontroller associated with the motor 32 of the polygon mirror 12 to makeany necessary adjustments to the rotational speed of the polygon mirror12, for example. The controller may regulate or stabilize the rotationalspeed of the polygon mirror 12 so that the rotational speed issubstantially constant. For example, the polygon mirror 12 may berotated at a rotational speed of approximately 150 Hz (150 revolutionsper second), and the rotational speed may be stabilized so that itvaries by less than or equal to 1% (e.g., 150 Hz±1.5 Hz), 0.1%, 0.05%,0.01%, or 0.005%.

The planar mirror 14 is pivotally mounted along a planar support shaft34 that extends orthogonal to the polygon mirror axle 30. The planarmirror 14 preferably has a body 50 defined by a plurality of rib-likemembers 52 that form a honeycomb-like structure, supporting a finishedplanar reflective surface 54 (see FIG. 20). The center of gravity of theplanar mirror 14 is closer to the reflective surface 54 than to an edgeof the ribbed or honeycomb body 50 opposite the reflective surface 54.The planar mirror 14 may be made from any suitable material, such as forexample, metal (e.g., aluminum), ceramic polymer, or carbon fiber.

The reflective surface 54 of the planar mirror 14 preferably has a widththat is greater than a width of each of the reflective surfaces 18-24 ofthe rotatable polygon mirror 12, measured along a common axis. In theembodiment illustrated in FIGS. 1-25, the width of the planar mirror 14is measured in the horizontal dimension, i.e., along a scan line (seeFIG. 19). The width of each surface of the polygon mirror 12 can bemeasured along an axis that is parallel to the pivot axis of the planarmirror 14 in a certain orientation of the polygon mirror 12. The widthof the planar mirror 14 effectively determines the horizontal range,i.e., FOR_(H).

For the same polygon mirror 12, the FOR_(H) of the sensor unit 10 can beincreased by selecting a wider planar mirror. For example, the planarmirror of width 5.3 inches can provide a FOR_(H) of about 100 degrees.As a more specific example, the lidar sensor unit 10 can have two eyes,each with an FOR_(H) of 52 degrees, and a two-degree overlap between theeyes. The planar mirror of width 8.1 inches can provide a FOR_(H) ofabout 130 degrees. The possibility of increasing the FOR_(H) of thelidar sensor unit 10 by selecting a planar mirror of a different widthfor the same polygon mirror provides for a modular optical design.

As illustrated in FIG. 14, the first wall 26 of rotatable polygon mirror12 has a major diameter D1 that extends from the corner of two adjacentfinished reflective surfaces 18, 20 to a corner of two opposite finishedreflective surfaces 22, 24, and a minor diameter D2 that extends from acenter of one of the finished reflective surfaces 18 to a center of anopposite one of the finished reflective surfaces 22. A limiting factorin optimizing the minimal height and width of the lidar sensor unit 10is the necessary spacing between the finished reflective surfaces 18-24of the rotatable polygon mirror 12 and the planar mirror 14. Bystrategically removing portions of material from the block 16, it isfound that the dimensional difference between the major diameter D1 andthe minor diameter D2 need not serve as a constraint to the dimensioningof the overall lidar sensor unit 10. As illustrated in FIGS. 10-12, aplurality of chamfers 36, 38, 40, 42 are formed in the block 16, each ofthe chamfers being bounded by a pair of adjacent reflective surfaces18-24 and the second wall 28. Each of these chamfers 36-42 is preferablycut at an angle of 45° to the adjacent finished reflective surfaces andsecond wall 28. However, the chamfers may be formed at a different angleto these adjacent surfaces.

The planar mirror 14 is located on the side of the rotatable polygonmirror 12 closest to the second wall 28. The chamfers 36-42 effectivelyreduce the major diameter of the rotatable polygon mirror 12 to amaximum dimension D1′ (see FIG. 13) that is less than D1, such that aminimum distance between the rotatable polygon mirror 12 and the planarmirror 14 can be maintained while still minimizing the overall heightand width dimensions of the lidar sensor unit 10. The reflectivesurfaces 18-24 of the polygon mirror 12 can be manufactured usingsurface replication techniques, and coarse as well as fine balancingtechniques can be applied to the polygon mirror 12, as discussed below.

By way of example only, and referring back to FIG. 1, the lidar sensorunit 10 may be provided in a housing that includes a shell roof 56, afirst shell side wall 58, a second shell side wall 60, and a shell floor62. Depending on where the lidar sensor unit 10 is mounted on a vehicle,one or more of the surfaces of the housing could coincide with anexternal or interior surface of a vehicle, as discussed below.

The housing of the lidar sensor unit 10 is configured so that rotationof the polygon mirror 12 imparts a flow of air through the housing toprovide cooling to components enclosed within the housing. The air flowmay be a laminar flow, a turbulent flow, or any suitable combinationthereof. Such cooling need not be the exclusive means of cooling of theinterior components of the lidar sensor unit 10. For instance, one ormore of a fan, cooling fins, or a heat exchanger can be used to moderatethe temperature of the components of the lidar sensor unit 10. However,the air flow within the housing and the aerodynamic construction of thecomponents of the polygon mirror 12 of the lidar sensor unit 10preferably account for a substantial portion of the temperaturemitigation of the lidar sensor unit 10, even when any one or more of afan, cooling fins, or a heat exchanger are additionally provided in thehousing to supplement cooling. A substantial portion of the temperaturemitigation of the lidar sensor unit 10 may be a majority of the cooling,at least 75% of the cooling, at least 80% of the cooling, at least 85%of the cooling, at least 90% of the cooling, at least 95% of thecooling, at least 98% of the cooling, or at least 99% of the cooling.Alternatively, the air flow within the housing and the aerodynamicconstruction of the components of the polygon mirror 12 of the lidarsensor unit 10 may be relied upon to supply all of the cooling when atleast one of the temperature within the housing of the lidar sensor unit10 or the ambient temperature is below a certain predefined temperature,and if the at least one of the temperature within the housing of thelidar sensor unit 10 or the ambient temperature exceeds the predefinedtemperature, the air flow within the housing and the aerodynamicconstruction of the components of the polygon mirror 12 of the lidarsensor unit 10 may be supplemented by at least one or more of a fan,cooling fins, or a heat exchanger to provide cooling. In someimplementations, the polygon mirror 12 may be at least partiallysurrounded or enclosed by a shroud that may act to aid or direct the aircirculation provided by the polygon mirror 12. The shroud may include adust collector (e.g., a filter) configured to remove dust fromcirculating air.

The planar mirror 14 is actuated by a drive system such as thatillustrated in FIG. 15. The drive system includes a drive motor 64,which, by way of example, may be a brushless FAULHABER (trademark) drivemotor, a plurality of pulleys 66, 68, 70, one of the pulleys 68 axiallyaligned with an encoder 72, and a drive belt 74 translating rotationalmotion of one of the pulleys 68 driven directly by the drive motor 64 tothe other two pulleys 68, 70. The drive motor 64 may be secured to theshell roof 56 by a shell roof motor mount 76.

As discussed in more detail below, the lidar sensor unit 10 according tosome implementations includes optical elements configured to receivelight signals such as intermittent pulses or continuous beams from alaser, and direct the light signals toward the active reflectivesurface(s) of the rotatable polygon mirror 12. The optical elements caninclude a fiber-optic cable via which the lidar sensor unit 10 iscoupled to the laser, and a collimator or a lens to produce a collimatedfree-space output beam. Referring to FIG. 1, one or several outputcollimators 77 in an example implementation direct light pulses ofrespective output beams toward the rotatable polygon mirror 12 viaapertures of the overlap doughnut mirror 79. However, in otherimplementations considered in more detail with reference to FIGS. 23-25,output collimators of the lidar sensor unit 10 and an aperture-freeoverlap mirror implement an off-axis illumination technique. The mirror79, or an aperture-free mirror oriented similar to the mirror 79, alsocan be referred to as a superposition mirror or beam-combiner mirror.

If desired, the housing of the lidar sensor unit 10 can enclose a laseror multiple lasers configured to generate output beams with differentwavelengths. Further, a diffractive optical element (DOE) beam splitter46 can be used to split a beam output by the laser (or the beam receivedfrom a remote laser via a fiber-optic cable) into at least two beams.The beams may have distinct wavelengths from one another. The beamsplitter 46 in general can be any suitable holographic element, apixelator, diffractive element, etc.

In any case, the one or several collimators 77 direct pulses of light atthe reflective surfaces of the rotatable polygon mirror 12, which inturn reflect the pulses toward the planar reflective surface 54. Therotation of the rotatable polygon mirror 12 and the planar mirror 14achieve the horizontal and vertical scan effect of the lidar sensor unit10.

An optic base 44 (see FIGS. 1 & 2) can enclose a receiver with one ormore detectors. Depending on whether the scanner 11 utilizes a singlereflective surface of the polygon mirror 12 or two reflective surfaces,the sensor unit 10 can include a single optic base 44 or two optic bases44. As illustrated in FIG. 21, the optic base 44 can enclose a lens 80to focus an input beam onto an assembly 81 including an optical filterand a detector, discussed in more detail below.

The axis of rotation of the polygon mirror 12 may be aligned with anorientation of predominant motion of the vehicle in which the lidarsystem 10 operates. For instance, a front-facing lidar system 10 may beoriented such that the axis of rotation of the polygon mirror 12 isaligned with a longitudinal axis of the vehicle. Such an orientation mayserve to reduce adverse effects of vibration, acceleration, anddeceleration. These techniques are illustrated in FIG. 30.

The planar mirror 14 may be configured so as to pivot over a range ofallowable motion larger than a range corresponding to the verticalangular dimension of the field of regard, so as to define a maximumrange of allowable motion larger than a range within which the planarmirror 14 pivots during a scan. A controller associated with the planarmirror 14 selects different portions of the maximum range of allowablemotion as the range within which the second mirror pivots, in accordancewith modifications of the scan pattern. In particular, to modify atleast one of a scan pattern or a scan rate, a controller associated withthe motor 32 of the polygon mirror 12 can be configured to cause themotor 32 to vary the speed of rotation of the polygon mirror 12, causethe drive motor 64 to vary the vary the oscillation of the planar mirror14, or both. The controller can be associated with both the polygonmirror 12 and the planar mirror 14. The controller may be configured tomodify the scan pattern on a frame-by-frame basis, each framecorresponding to a complete scan of the field of regard of the lidarsystem 10. In some implementations, the oscillation of the planar mirror14 may be varied (e.g., to change the vertical angular dimension of thefield of regard), and the rotational speed of the polygon mirror 12 maybe regulated or stabilized so that the polygon mirror 12 rotates at asubstantially constant speed.

With reference to FIGS. 1-5, the polygon mirror 12 in someimplementations can be disposed between a third of the way from a firstedge of the y-scan mirror 14 and a third of the way from a second edgeof the y-scan mirror 14. In a particular embodiment, the polygon mirroraxis bisects a length of the y-scan mirror 14.

Besides the lidar sensor unit 10, the scanner 11 can operate in anysuitable optical system to scan the FOR. The scanner 11 in an embodimentincludes the polygon mirror 12 rotatable about a polygon mirror axis toscan the FOR of the optical system along a horizontal dimension, thepolygon mirror 12 including a plurality of reflective surfaces 18-24being angularly offset from one another along a periphery of the block16; and a y-scan mirror 14 pivotable along a pivot axis orthogonal tothe polygon mirror axis to scan the FOR of the optical system along avertical dimension. The width of the y-scan mirror 14 is larger than thewidth of each of the reflective surfaces 18-24 of the polygon mirror 12.The polygon mirror 12 reflects light incident on one of the reflectivesurfaces toward the y-scan mirror 14. The width of the y-scan mirror 14ultimately determines the scan range along the horizontal dimension.

II. Propagation of Input and Output Light Beams Through the Lidar SensorUnit

FIG. 22 schematically depicts an example implementation of the lidarsensor unit 10 that includes the doughnut overlap mirror 79 discussedabove. In this implementation, an output beam 82 travels from the outputcollimator 77 through an aperture of the overlap mirror 79 and impingeson one of the reflective surfaces of the polygon mirror 12. Thereflective surface of the polygon mirror 12 reflects the output beam 82to a location on the planar mirror 14 that depends on the currentorientation of the polygon mirror 12, thereby defining the current anglewithin the FOR_(H). The planar mirror 14 then directs the output beam 82out of the lidar sensor unit 10 at a vertical angle that depends on thecurrent orientation of planar mirror 14, thereby defining the currentangle within the FOR_(V). In this manner, the scanner 11 can disperselight pulses of the output beam 82 across the FOR of the lidar sensorunit 10. An input beam 83 travels to the planar mirror 14, which directsthe input beam 83 to the polygon mirror 12, which in turn directs theinput beam 83 to the overlap mirror 79.

Now referring to FIG. 23, an assembly 86 is generally similar to theassembly of FIG. 22. However, unlike the overlap doughnut mirror 79, anoverlap mirror 90A does not include an aperture, and an outputcollimator 92A directs an output beam by the side of the overlap mirror90A toward a reflective surface 12-1 of the polygon mirror 12. An outputcollimator 94A can direct another output beam by the side of the overlapmirror 90A toward the same reflective surface 12-1 of the polygon mirror12. The output collimators 92A and 94A can be configured to emit pulseshaving different wavelengths, and two respective detectors can beconfigured to detect the corresponding return pulses in a shared inputbeam reflected by the surface 12-1. In this manner, a lidar sensor unitthat includes the assembly 86 can generate values for two pixels in acertain scan line within a same ranging event. Alternatively, the outputcollimators 92A and 94A can launch the output beams with a particularspatial or angular offset, and the two input beams have a correspondingspatial or angular offset, with the wavelength of the pulses emitted bythe output collimators 92A and 94A being the same.

Further, in the example implementation of FIG. 23, the assembly 86includes output collimators 92B and 94B mechanically aimed at a surface12-2 of the polygon mirror 12. The output collimators 92B and 94B alsodirect output beams by the side of the corresponding overlap mirror 90B.Similar to the overlap mirror 90A, the overlap mirror 90B does notinclude an aperture.

The input beam which the reflective surface 12-1 directs to the overlapmirror 90A can be regarded as the first eye of the lidar sensor unit,and the input beam which the reflective surface 12-2 directs to theoverlap mirror 90B can be regarded as the second eye of the lidar sensorunit. The assembly 86 thus implements off-axis illumination for botheyes of the lidar sensor unit.

For further clarity, FIGS. 24 and 25 illustrate example paths alongwhich input and output beams travel in the sensor unit 10 and, inparticular, the scanner 11. As discussed in more detail below, an inputbeam typically contains only a relatively small portion of the energy ofan output beam. A receiver field of view (FOV) may define a largerangular cone over which the receiver detects light as compared to thelight-source FOV, or the angular cone illuminated by the light source.Accordingly, FIGS. 24 and 25 illustrate input and output beams of ascones of different sizes, but neither the sizes of the cones nor thedegrees of divergence of these cones are drawn to scale.

In the scenario of FIG. 24, the input beam 102A first impinges on thereflective surface of the planar mirror 14, which reflects the inputbeam 102A toward the reflective surface of the polygon mirror 12, whichin turn reflects the input beam 102B toward the overlap mirror 90A. Theoverlap mirror 90A then directs the input beam 102A toward a lens 104A,which focuses the input beam 102A on an active region 106A of a receiver108A. For a given operational state, the current orientation of thepolygon mirror 12 defines the horizontal position of the receiver fieldof view FOV_(A) within the FOR of the sensor unit 10, and the currentorientation of the planar mirror 14 defines the vertical position of theFOV_(A) within the FOR. An input beam 102B in meantime impinges on theplanar mirror 14 at a different location. The planar mirror 14 directsthe input beam 102B to a different surface of the polygon mirror 12,which in turn directs the input beam 102B to an assembly including anoverlap mirror, a lens, an active region of a receiver, etc. (notillustrated to avoid clutter) disposed on the opposite side of thepolygon mirror 12 from the components 90A, 104A, etc.

The output beams according to these implementations are scannedsynchronously because these beams reflect off the same mirrors 12 and14. In other words, the output beams are scanned at approximately thesame scanning rate across the field of regard, and the input beamsmaintain approximately the same angular separation. For example, bothoutput beams may scan horizontally across the field of regard atapproximately 600 radians/sec, and the two output beams may have asubstantially fixed angular separation of approximately 20 degrees. Inaddition to the two output beams being scanned synchronously withrespect to each other, each receiver FOV is also scanned synchronouslywith its respective light-source FOV.

As discussed in more detail below, a lidar system can use the inputbeams 102A and 102B to generate two pixels during the same rangingevent, with an integer or non-integer separation between the pixels.Further, in some implementations, each of the input beams 102A and 102Bis made up of two beams of light corresponding to two output beams ofdifferent wavelengths, λ₁ and λ₂, and accordingly can be used to producetwo pixels (e.g., an odd pixel and an even pixel) rather than a singlepixel during a single ranging event. The lidar sensor unit 10 thus canproduce the total of four pixels per ranging event. As a more specificexample, a DOE or another suitable element can impart to a pulse oflight a relatively small angular separation into pulses of wavelengthsλ₁ and λ₂, so that the distance between the light pulses of wavelengthsλ₁ and λ₂ at the maximum range of the lidar system corresponds to thewidth of multiple pixels. The DOE may split the pulse before directingthe resulting output beams to the polygon mirror, or the DOE may bedisposed downrange of the mirrors 12 and 14 and split a pulse afterpropagation through the scanner.

In another example implementation, the input beam 102A includes twocomponent input beams of the same wavelength, which are substantiallyoverlapped spatially but have a small angular offset (e.g., betweenapproximately 0.1 and 2 degrees) with respect to one another. When thetwo component input beams pass through the lens 104A, the angular offsetresults in the two beams being focused on two separate spots, which maybe separated by approximately 0.4 to 2 mm. In this manner, the angularoffset between the beams results in a spatial separation after passingthrough the lens.

FIG. 25 illustrates an example spatial arrangement of the fields of viewof the input beam 102A and output beams 110A and 110B. The beams 102A,110A, and 110B are mechanically aimed so as to minimize the resulting“footprints” on the mirrors 14 and 12. Thus, the beams are adjacent toeach other on the reflective surfaces of the mirrors 12 and 14. Further,in accordance with off-axis illumination techniques, the output beams110A and 110B are directed at a reflective surface of the polygon mirror12 so as to be not entirely coaxial with the input beam 102A(illustrated in FIG. 25 in an exaggerated manner).

In contrast to the implementation of FIGS. 23-25, the output beam 82 andthe input beam 83 in FIG. 22 are more aligned with each other, and maybe substantially coaxial. The output beam 82 and input beam 83 may atleast partially overlap or share a common propagation axis, so that theoutput beam 82 and input beam 83 travel along substantially the sameoptical path (albeit in opposite directions). As the lidar system scansthe output beam 82 across a field of regard, the input beam 83 mayfollow along with the output beam 82, so that the coaxial relationshipbetween the two beams is maintained.

Referring again to FIG. 25, the output beams of light 110A and 110Bemitted by the light source (such as a light source 122A, discussedbelow with reference to FIGS. 26A and 26B) is a collimated optical beamwith any suitable beam divergence, such as a divergence of approximately0.1 to 3.0 milliradian (mrad). Divergence of the output beams 110A and110B may refer to an angular measure of an increase in beam size (e.g.,a beam radius or beam diameter) as the output beams 110A and 110B travelaway from the lidar system. The output beams 110A and 110B may have asubstantially circular cross section with a beam divergencecharacterized by a single divergence value. For example, the outputbeams 110A and 110B with a circular cross section and a divergence of 1mrad may have a beam diameter or spot size of approximately 10 cm at adistance of 100 m from the lidar system. In some implementations, theoutput beams 110A and 110B may be an astigmatic beam or may have asubstantially elliptical cross section and may be characterized by twodivergence values. As an example, the output beams 110A and 110B mayhave a fast axis and a slow axis, where the fast-axis divergence isgreater than the slow-axis divergence. As another example, the outputbeams 110A and 110B may be an astigmatic beam with a fast-axisdivergence of 2 mrad and a slow-axis divergence of 0.5 mrad.

The output beams 110A and 110B may be unpolarized or randomly polarized,may have no specific or fixed polarization (e.g., the polarization mayvary with time), or may have a particular polarization (e.g., the outputbeams 110A and 110B may be linearly polarized, elliptically polarized,or circularly polarized). As an example, the light source may producelinearly polarized light, and the lidar system may include aquarter-wave plate that converts this linearly polarized light intocircularly polarized light. The lidar system may transmit the circularlypolarized light as the output beams 110A and 110B, and receive the inputbeam(s) 102A, which may be substantially or at least partiallycircularly polarized in the same manner as the output beams 110A and110B (e.g., if the output beams 110A and 110B are right-hand circularlypolarized, then the input beam 102A may also be right-hand circularlypolarized). The input beam 102A may pass through the same quarter-waveplate (or a different quarter-wave plate), resulting in the input beam102A being converted to linearly polarized light which is orthogonallypolarized (e.g., polarized at a right angle) with respect to thelinearly polarized light produced by light source 110. As anotherexample, the lidar system may employ polarization-diversity detectionwhere two polarization components are detected separately. The outputbeams 110A and 110B may be linearly polarized, and the lidar system maysplit the input beam 102A into two polarization components (e.g.,s-polarization and p-polarization) which are detected separately by twophotodiodes (e.g., a balanced photoreceiver that includes twophotodiodes).

The scanner 11 can scan each of the first beam of light and the secondbeam of light so as to define a respective field of regard approximately60 degrees wide. Depending on the implementation, the fields of regardcan have a relatively large overlap (e.g., 20 degrees, 30 degrees, 40degrees), a relatively small overlap (e.g., one degree, two degrees,three degrees, four degrees, five degrees), or no overlap. Dynamicmodifications to the fields of regard are discussed in more detailbelow. The overlap region may be oriented in a direction of travel of avehicle on which the lidar system 10 is deployed.

III. Operation of a Lidar System

Next, FIG. 26A illustrates an example lidar system 120A in which all orsome of the components of lidar sensor unit 10 can be implementedaccording to a single-eye configuration. The lidar system 120A may bereferred to as a laser ranging system, a laser radar system, a LIDARsystem, a lidar sensor, or a laser detection and ranging (LADAR orladar) system. The lidar system 120A may include a light source 122A, amirror 124A (referred to as overlap mirror, superposition mirror, orbeam-combiner mirror), a scanner 11, a receiver 128A, and a controller130 equipped with a memory unit 132. In some implementations, the lidarsystem 120A also can include one or more sensors 134 such as atemperature sensor, a moisture sensor, etc.

The scanner 11 may be referred to as a beam scanner, optical scanner, orlaser scanner. The scanner 11 may be implemented as discussed above withreference to FIGS. 1-25 and include a polygon mirror 12, a planar mirror14, and corresponding motors to drive the rotation of the polygon mirror12 and the oscillation of the planar mirror 14.

Depending on the implementation, the controller 130 may include one ormore processors, an application-specific integrated circuit (ASIC), afield-programmable gate array (FPGA), and/or other suitable circuitry.The non-transitory computer-readable memory 132 of the controller 130can be configured to store instructions executable by the controller 130as well as data which the controller 130 can produce based on thesignals from the components of the system 120A and/or provide to thesecomponents. The memory 132 can include volatile (e.g., RAM) and/ornon-volatile (e.g., flash memory, a hard disk) components. The data thecontroller 130 generates during operation and stores in the memory 132can include pixel data and other results of analyzing characteristics ofthe target 160, alarm data (e.g., readings from the sensors 134 thatexceed certain predefined thresholds), and the configuration data thecontroller 130 can retrieve from the memory 132 during operation caninclude definitions of various scan patterns, for example. Alternativelyor additionally to the memory 132, the controller 130 can be configuredto access memory disposed remotely relative to the lidar system 120A inthe vehicle controller (see below) or even memory disposed remotelyrelative to the vehicle, such as on a network server. In addition tocollecting data from receiver 128A, the controller 130 can providecontrol signals to and, in some implementations, receive diagnosticsdata from, the light source 122A, the one or more sensors 134, and thescanner 11 via communication links 136.

In some implementations, the light source 122A can be an outputcollimator similar to the output collimator(s) 77 discussed above, e.g.,a lens rigidly coupled to an end of a fiber-optic cable, with the otherend of the fiber-optic cable coupled to a laser disposed remotelyrelative to the scanner 11. Examples of such configurations arediscussed in more detail below with reference to FIGS. 32 and 33. Inother implementations, the light source 122A can be an assembly thatincludes a laser.

The light source 122A thus may include, or be optically coupled to, alaser which emits light having a particular operating wavelength in theinfrared, visible, or ultraviolet portions of the electromagneticspectrum. As a more specific example, the light source 122A may includea laser with an operating wavelength between approximately 1.2 μm and1.7 μm.

In operation, the light source 122A emits an output beam of light 150Awhich may be continuous-wave, pulsed, or modulated in any suitablemanner for a given application. The output beam of light 150A isdirected downrange toward a remote target 160 located a distance D fromthe lidar system 120A and at least partially contained within a field ofregard of the system 120A. Depending on the scenario and/or theimplementation of the lidar system 120A, the distance D can be between 1m and 1 km, for example.

Once the output beam 150A reaches the downrange target 160, the target160 may scatter or, in some cases, reflect at least a portion of lightfrom the output beam 150A, and some of the scattered or reflected lightmay return toward the lidar system 120A. In the example of FIG. 26A, thescattered or reflected light is represented by input beam 164A, whichpasses through the scanner 11. The input beam 164A passes through thescanner 11 to the mirror 124A. The mirror 124A in turn directs the inputbeam 164A to the receiver 128A. The input beam 164A may contain only arelatively small fraction of the light from the output beam 150A. Forexample, the ratio of average power, peak power, or pulse energy of theinput beam 164A to average power, peak power, or pulse energy of theoutput beam 150A may be approximately 10⁻¹, 10⁻², 10⁻³, 10⁻⁴, 10⁻⁵,10⁻⁶, 10⁻⁷, 10⁻⁸, 10⁻⁹, 10⁻¹⁰, 10⁻¹¹, or 10⁻¹². As another example, if apulse of the output beam 150A has a pulse energy of 1 microjoule (μJ),then the pulse energy of a corresponding pulse of the input beam 164Amay have a pulse energy of approximately 10 nanojoules (nJ), 1 nJ, 100picojoules (pJ), 10 pJ, 1 pJ, 100 femtojoules (fJ), 10 fJ, 1 fJ, 100attojoules (aJ), 10 aJ, or 1 aJ.

The output beam 150A may be referred to as a laser beam, light beam,optical beam, emitted beam, or just beam; and the input beam 164A may bereferred to as a return beam, received beam, return light, receivedlight, input light, scattered light, or reflected light. As used herein,scattered light may refer to light that is scattered or reflected by thetarget 160. The input beam 164A may include light from the output beam150A that is scattered by the target 160, light from the output beam150A that is reflected by the target 160, or a combination of scatteredand reflected light from target 160A. The input beam 164A also caninclude “passive” light signals, or light from various other sources andof various wavelengths scattered by the target 160.

The operating wavelength of a lidar system 120A may lie, for example, inthe infrared, visible, or ultraviolet portions of the electromagneticspectrum. The Sun also produces light in these wavelength ranges, andthus sunlight can act as background noise which can obscure signal lightdetected by the lidar system 120A. This solar background noise canresult in false-positive detections or can otherwise corruptmeasurements of the lidar system 120A, especially when the receiver 128Aincludes SPAD detectors (which can be highly sensitive).

Generally speaking, the light from the Sun that passes through theEarth's atmosphere and reaches a terrestrial-based lidar system such asthe system 120A can establish an optical background noise floor for thissystem. Thus, in order for a signal from the lidar system 120A to bedetectable, the signal must rise above the background noise floor. It isgenerally possible to increase the signal-to-noise (SNR) ratio of thelidar system 120A by raising the power level of the output beam 150A,but in some situations it may be desirable to keep the power level ofthe output beam 150A relatively low. For example, increasing transmitpower levels of the output beam 150A can result in the lidar system 120Anot being eye-safe.

In some implementations, the lidar system 120A operates at one or morewavelengths between approximately 1400 nm and approximately 1600 nm. Forexample, the light source 122A may produce light at approximately 1550nm.

In some implementations, the lidar system 120A operates at frequenciesat which atmospheric absorption is relatively low. For example, thelidar system 120A can operate at wavelengths in the approximate rangesfrom 980 nm to 1110 nm or from 1165 nm to 1400 nm.

In other implementations, the lidar system 120A operates at frequenciesat which atmospheric absorption is high. For example, the lidar system120A can operate at wavelengths in the approximate ranges from 930 nm to980 nm, from 1100 nm to 1165 nm, or from 1400 nm to 1460 nm.

According to some implementations, the lidar system 120A can include aneye-safe laser, or the lidar system 120A can be classified as aneye-safe laser system or laser product. An eye-safe laser, laser system,or laser product may refer to a system with an emission wavelength,average power, peak power, peak intensity, pulse energy, beam size, beamdivergence, exposure time, or scanned output beam such that emittedlight from the system presents little or no possibility of causingdamage to a person's eyes. For example, the light source 122A or thelidar system 120A may be classified as a Class 1 laser product (asspecified by the 60825-1 standard of the International ElectrotechnicalCommission (IEC)) or a Class I laser product (as specified by Title 21,Section 1040.10 of the United States Code of Federal Regulations (CFR))that is safe under all conditions of normal use. In someimplementations, the lidar system 120A may be classified as an eye-safelaser product (e.g., with a Class 1 or Class I classification)configured to operate at any suitable wavelength between approximately1400 nm and approximately 2100 nm. In some implementations, the lightsource 122A may include a laser with an operating wavelength betweenapproximately 1400 nm and approximately 1600 nm, and the lidar system120A may be operated in an eye-safe manner. In some implementations, thelight source 122A or the lidar system 120A may be an eye-safe laserproduct that includes a scanned laser with an operating wavelengthbetween approximately 1530 nm and approximately 1560 nm. In someimplementations, the lidar system 120A may be a Class 1 or Class I laserproduct that includes a fiber laser or solid-state laser with anoperating wavelength between approximately 1400 nm and approximately1600 nm.

The receiver 128A may receive or detect photons from the input beam 164Aand generate one or more representative signals. For example, thereceiver 128A may generate an output electrical signal 145A that isrepresentative of the input beam 164. The receiver 128A may send theelectrical signal to the controller 130. The controller 130 can beconfigured to analyze one or more characteristics of the electricalsignal 145A to determine one or more characteristics of the target 160,such as its distance downrange from the lidar system 120A. Moreparticularly, the controller 130 may analyze the time of flight or phasemodulation for the beam of light 150A transmitted by the light source122A. If the lidar system 120A measures a time of flight of T (e.g., Trepresents a round-trip time of flight for an emitted pulse of light totravel from the lidar system 120A to the target 160 and back to thelidar system 120A), then the distance D from the target 160 to the lidarsystem 120A may be expressed as D=c·T/2, where c is the speed of light(approximately 3.0×10⁸ m/s).

As a more specific example, if the lidar system 120A measures the timeof flight to be T=300 ns, then the lidar system 120A can determine thedistance from the target 160 to the lidar system 120A to beapproximately D=45.0 m. As another example, the lidar system 120Ameasures the time of flight to be T=1.33 μs and accordingly determinesthat the distance from the target 160 to the lidar system 120A isapproximately D=199.5 m. The distance D from lidar system 120A to thetarget 160 may be referred to as a distance, depth, or range of thetarget 160. As used herein, the speed of light c refers to the speed oflight in any suitable medium, such as for example in air, water, orvacuum. The speed of light in vacuum is approximately 2.9979×10⁸ m/s,and the speed of light in air (which has a refractive index ofapproximately 1.0003) is approximately 2.9970×10⁸ m/s.

The target 160 may be located a distance D from the lidar system 120Athat is less than or equal to a maximum range R_(MAX) of the lidarsystem 120A. The maximum range R_(MAX) (which also may be referred to asa maximum distance) of a lidar system 120A may correspond to the maximumdistance over which the lidar system 120A is configured to sense oridentify targets that appear in a field of regard of the lidar system120A. The maximum range of lidar system 120A may be any suitabledistance, such as for example, 25 m, 50 m, 100 m, 200 m, 500 m, or 1 km.As a specific example, a lidar system with a 200-m maximum range may beconfigured to sense or identify various targets located up to 200 maway. For a lidar system with a 200-m maximum range (R_(MAX)=200 m), thetime of flight corresponding to the maximum range is approximately 2.R_(MAX)/c≅1.33 μs.

In some implementations, the light source 122A, the scanner 11, and thereceiver 128A are packaged together within a single housing 165, whichmay be a box, case, or enclosure that holds or contains all or part of alidar system 120A. The housing 165 can include at least some of thehousing components (the shell roof 56, the shell side wall 58, etc.)discussed above. In the example of FIG. 26A, the housing 165 includes awindow 167 through which the beams 150A and 164A pass. In one exampleimplementation, the lidar-system housing 165 contains the light source122A, the overlap mirror 124A, the scanner 11, and the receiver 128A ofthe lidar system 120A. The controller 130 may reside within the samehousing 165 as the components 122A, 11, 128A or the controller 130 mayreside remotely from the housing 165.

Moreover, in some implementations, the housing 165 includes multiplelidar sensor units, each including a respective scanner and a receiver.Depending on the particular implementation, each of the multiple lidarsensor units can include a separate light source or a common lightsource. The multiple lidar sensor units can be configured to covernon-overlapping adjacent fields of regard or partially overlappingfields of regard, depending on the implementation.

The housing 165 may be an airtight or watertight structure that preventswater vapor, liquid water, dirt, dust, or other contaminants fromgetting inside the housing 165. The housing 165 may be filled with a dryor inert gas, such as for example dry air, nitrogen, or argon. Thehousing 165 may include one or more electrical connections for conveyingelectrical power or electrical signals to and/or from the housing.

The window 167 may be made from any suitable substrate material, such asfor example, glass or plastic (e.g., polycarbonate, acrylic,cyclic-olefin polymer, or cyclic-olefin copolymer). The window 167 mayinclude an interior surface (surface A) and an exterior surface (surfaceB), and surface A or surface B may include a dielectric coating havingparticular reflectivity values at particular wavelengths. A dielectriccoating (which may be referred to as a thin-film coating, interferencecoating, or coating) may include one or more thin-film layers ofdielectric materials (e.g., SiO₂, TiO₂, Al₂O₃, Ta₂O₅, MgF₂, LaF₃, orAlF₃) having particular thicknesses (e.g., thickness less than 1 μm) andparticular refractive indices. A dielectric coating may be depositedonto surface A or surface B of the window 167 using any suitabledeposition technique, such as for example, sputtering or electron-beamdeposition.

The dielectric coating may have a high reflectivity at a particularwavelength or a low reflectivity at a particular wavelength. Ahigh-reflectivity (HR) dielectric coating may have any suitablereflectivity value (e.g., a reflectivity greater than or equal to 80%,90%, 95%, or 99%) at any suitable wavelength or combination ofwavelengths. A low-reflectivity dielectric coating (which may bereferred to as an anti-reflection (AR) coating) may have any suitablereflectivity value (e.g., a reflectivity less than or equal to 5%, 2%,1%, 0.5%, or 0.2%) at any suitable wavelength or combination ofwavelengths. In particular embodiments, a dielectric coating may be adichroic coating with a particular combination of high or lowreflectivity values at particular wavelengths. For example, a dichroiccoating may have a reflectivity of less than or equal to 0.5% atapproximately 1550-1560 nm and a reflectivity of greater than or equalto 90% at approximately 800-1500 nm.

In some implementations, surface A or surface B has a dielectric coatingthat is anti-reflecting at an operating wavelength of one or more lightsources 122A contained within enclosure 165. An AR coating on surface Aand surface B may increase the amount of light at an operatingwavelength of light source 122A that is transmitted through the window167. Additionally, an AR coating at an operating wavelength of the lightsource 120A may reduce the amount of incident light from output beam150A that is reflected by the window 167 back into the housing 165. Inan example implementation, each of surface A and surface B has an ARcoating with reflectivity less than 0.5% at an operating wavelength oflight source 122A. As an example, if the light source 122A has anoperating wavelength of approximately 1550 nm, then surface A andsurface B may each have an AR coating with a reflectivity that is lessthan 0.5% from approximately 1547 nm to approximately 1553 nm. Inanother implementation, each of surface A and surface B has an ARcoating with reflectivity less than 1% at the operating wavelengths ofthe light source 110. For example, if the housing 165 encloses twosensor heads with respective light sources, the first light source emitspulses at a wavelength of approximately 1535 nm and the second lightsource emits pulses at a wavelength of approximately 1540 nm, thensurface A and surface B may each have an AR coating with reflectivityless than 1% from approximately 1530 nm to approximately 1545 nm.

The window 167 may have an optical transmission that is greater than anysuitable value for one or more wavelengths of one or more light sources122A contained within the housing 165. As an example, the window 167 mayhave an optical transmission of greater than or equal to 70%, 80%, 90%,95%, or 99% at a wavelength of light source 122A. In one exampleimplementation, the window 167 can transmit greater than or equal to 95%of light at an operating wavelength of the light source 122A. In anotherimplementation, the window 167 transmits greater than or equal to 90% oflight at the operating wavelengths of the light sources enclosed withinthe housing 165.

Surface A or surface B may have a dichroic coating that isanti-reflecting at one or more operating wavelengths of one or morelight sources 122A and high-reflecting at wavelengths away from the oneor more operating wavelengths. For example, surface A may have an ARcoating for an operating wavelength of the light source 122A, andsurface B may have a dichroic coating that is AR at the light-sourceoperating wavelength and HR for wavelengths away from the operatingwavelength. A coating that is HR for wavelengths away from alight-source operating wavelength may prevent most incoming light atunwanted wavelengths from being transmitted through the window 167. Inone implementation, if light source 122A emits optical pulses with awavelength of approximately 1550 nm, then surface A may have an ARcoating with a reflectivity of less than or equal to 0.5% fromapproximately 1546 nm to approximately 1554 nm. Additionally, surface Bmay have a dichroic coating that is AR at approximately 1546-1554 nm andHR (e.g., reflectivity of greater than or equal to 90%) at approximately800-1530 nm and approximately 1570-1700 nm.

Surface B of the window 167 may include a coating that is oleophobic,hydrophobic, or hydrophilic. A coating that is oleophobic (or,lipophobic) may repel oils (e.g., fingerprint oil or other non-polarmaterial) from the exterior surface (surface B) of the window 167. Acoating that is hydrophobic may repel water from the exterior surface.For example, surface B may be coated with a material that is botholeophobic and hydrophobic. A coating that is hydrophilic attracts waterso that water may tend to wet and form a film on the hydrophilic surface(rather than forming beads of water as may occur on a hydrophobicsurface). If surface B has a hydrophilic coating, then water (e.g., fromrain) that lands on surface B may form a film on the surface. Thesurface film of water may result in less distortion, deflection, orocclusion of an output beam 150A than a surface with a non-hydrophiliccoating or a hydrophobic coating.

With continued reference to FIG. 26A, the light source 122A may includea pulsed laser configured to produce or emit pulses of light with acertain pulse duration. In an example implementation, the pulse durationor pulse width of the pulsed laser is approximately 10 picoseconds (ps)to 20 nanoseconds (ns). In another implementation, the light source 122Ais a pulsed laser that produces pulses with a pulse duration ofapproximately 1-4 ns. In yet another implementation, the light source122A is a pulsed laser that produces pulses at a pulse repetitionfrequency of approximately 100 kHz to 5 MHz or a pulse period (e.g., atime between consecutive pulses) of approximately 200 ns to 10 μs. Thelight source 122A may have a substantially constant or a variable pulserepetition frequency, depending on the implementation. As an example,the light source 122A may be a pulsed laser that produces pulses at asubstantially constant pulse repetition frequency of approximately 640kHz (e.g., 640,000 pulses per second), corresponding to a pulse periodof approximately 1.56 s. As another example, the light source 122A mayhave a pulse repetition frequency that can be varied from approximately500 kHz to 3 MHz. As used herein, a pulse of light may be referred to asan optical pulse, a light pulse, or a pulse, and a pulse repetitionfrequency may be referred to as a pulse rate.

In general, the output beam 150A may have any suitable average opticalpower, and the output beam 150A may include optical pulses with anysuitable pulse energy or peak optical power. Some examples of theaverage power of the output beam 150A include the approximate values of1 mW, 10 mW, 100 mW, 1 W, and 10 W. Example values of pulse energy ofthe output beam 150 include the approximate values of 0.1 μJ, 1 μJ, 10μJ, 100 μJ, and 1 mJ. Examples of peak power values of pulses includedin the output beam 150A are the approximate values of 10 W, 100 W, 1 kW,5 kW, 10 kW. An example optical pulse with a duration of 1 ns and apulse energy of 1 μJ has a peak power of approximately 1 kW. If thepulse repetition frequency is 500 kHz, then the average power of theoutput beam 150 with 1-μJ pulses is approximately 0.5 W, in thisexample.

The light source 122A may include a laser diode, such as a Fabry-Perotlaser diode, a quantum well laser, a distributed Bragg reflector (DBR)laser, a distributed feedback (DFB) laser, or a vertical-cavitysurface-emitting laser (VCSEL). The laser diode operating in the lightsource 122A may be an aluminum-gallium-arsenide (AlGaAs) laser diode, anindium-gallium-arsenide (InGaAs) laser diode, or anindium-gallium-arsenide-phosphide (InGaAsP) laser diode, or any othersuitable diode. In some implementations, the light source 122A includesa pulsed laser diode with a peak emission wavelength of approximately1400-1600 nm. Further, the light source 122A may include a laser diodethat is current-modulated to produce optical pulses.

In some implementation, the light source 122A includes a pulsed laserdiode followed by one or more optical-amplification stages. For example,the light source 122A may be a fiber-laser module that includes acurrent-modulated laser diode with a peak wavelength of approximately1550 nm, followed by a single-stage or a multi-stage erbium-doped fiberamplifier (EDFA) or erbium/ytterbium-doped fiber amplifier (EYDFA). Asanother example, the light source 122A may include a continuous-wave(CW) or quasi-CW laser diode followed by an external optical modulator(e.g., an electro-optic modulator), and the output of the modulator maybe fed into an optical amplifier. In yet other implementations, thelight source 122A may include a pulsed solid-state laser or a pulsedfiber laser.

The lidar system 120A also may include one or more optical componentsconfigured to condition, shape, filter, modify, steer, or direct theoutput beam 150A and/or the input beam 164. For example, lidar system120A may include one or more lenses, mirrors, filters (e.g., bandpass orinterference filters), beam splitters, polarizers, polarizing beamsplitters, wave plates (e.g., half-wave or quarter-wave plates),diffractive elements, or holographic elements. In some implementations,the lidar system 120A includes a telescope, one or more lenses, or oneor more mirrors to expand, focus, or collimate the output beam 150A orthe input beam 164A to a desired beam diameter or divergence. As anexample, the lidar system 120A may include one or more lenses to focusthe input beam 164A onto an active region of the receiver 128A. Asanother example, the lidar system 120A may include one or more flatmirrors or curved mirrors (e.g., concave, convex, or parabolic mirrors)to steer or focus the output beam 150A or the input beam 164A. Forexample, the lidar system 120A may include an off-axis parabolic mirrorto focus the input beam 164A onto an active region of receiver 128A.

In operation, the light source 122A may emit pulses of light which thescanner 11 scans across a FOR of lidar system 120A. The target 160 mayscatter one or more of the emitted pulses, and the receiver 128A maydetect at least a portion of the pulses of light scattered by the target160. Example techniques for selecting and dynamically modifying the FORusing the lidar sensor unit of this disclosure are discussed in moredetail below with reference to FIGS. 35-40.

The receiver 128A may be referred to as (or may include) aphotoreceiver, optical receiver, optical sensor, detector,photodetector, or optical detector. The receiver 128A in someimplementations receives or detects at least a portion of the input beam164A and produces an electrical signal that corresponds to the inputbeam 164A. For example, if the input beam 164A includes an opticalpulse, then the receiver 128A may produce an electrical current orvoltage pulse that corresponds to the optical pulse detected by thereceiver 128A. In an example implementation, the receiver 128A includesone or more avalanche photodiodes (APDs) or one or more single-photonavalanche diodes (SPADs). In another implementation, the receiver 128Aincludes one or more PN photodiodes (e.g., a photodiode structure formedby a p-type semiconductor and a n-type semiconductor) or one or more PINphotodiodes (e.g., a photodiode structure formed by an undoped intrinsicsemiconductor region located between p-type and n-type regions).

The receiver 128A may have an active region or anavalanche-multiplication region that includes silicon, germanium, orInGaAs. The active region of receiver 128A may have any suitable size,such as for example, a diameter or width of approximately 50-500 μm. Thereceiver 128 may include circuitry that performs signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection. For example, thereceiver 128A may include a transimpedance amplifier that converts areceived photocurrent (e.g., a current produced by an APD in response toa received optical signal) into a voltage signal. The receiver 128A maydirect the voltage signal to pulse-detection circuitry that produces ananalog or digital output signal 145A that corresponds to one or morecharacteristics (e.g., rising edge, falling edge, amplitude, orduration) of a received optical pulse. For example, the pulse-detectioncircuitry may perform a time-to-digital conversion to produce thedigital output signal 145A. The receiver 128A may send the electricaloutput signal 145A to the controller 130 for processing or analysis,e.g., to determine a time-of-flight value corresponding to a receivedoptical pulse.

The controller 130 may be electrically coupled or otherwisecommunicatively coupled to one or more of the light source 122A, thescanner 11, and the receiver 128A. The controller 130 may receiveelectrical trigger pulses or edges from the light source 122A, whereeach pulse or edge corresponds to the emission of an optical pulse bythe light source 122A. The controller 130 may provide instructions, acontrol signal, or a trigger signal to the light source 122A indicatingwhen the light source 122A should produce optical pulses. For example,the controller 130 may send an electrical trigger signal that includeselectrical pulses, where the light source 122A emits an optical pulse inresponse to each electrical pulse. Further, the controller 130 may causethe light source 122A to adjust one or more of the frequency, period,duration, pulse energy, peak power, average power, or wavelength of theoptical pulses produced by the light source 122A.

The controller 130 may determine a time-of-flight value for an opticalpulse based on timing information associated with when the pulse wasemitted by the light source 122A and when a portion of the pulse (e.g.,the input beam 164A) was detected or received by the receiver 128A. Thecontroller 130 may include circuitry that performs signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection.

As indicated above, the lidar system 120A may be used to determine thedistance to one or more downrange targets 160. By scanning the outputbeam 150A across a field of regard, the lidar system 120A can be used tomap the distance to a number of points within the field of regard. Eachof these depth-mapped points may be referred to as a pixel or a voxel. Acollection of pixels captured in succession (which may be referred to asa depth map, a point cloud, or a frame) may be rendered as an image ormay be analyzed to identify or detect objects or to determine a shape ordistance of objects within the FOR. For example, a depth map may cover afield of regard that extends 60° horizontally and 15° vertically, andthe depth map may include a frame of 100-2000 pixels in the horizontaldirection by 4-400 pixels in the vertical direction.

The lidar system 120A may be configured to repeatedly capture orgenerate point clouds of a field of regard at any suitable frame ratebetween approximately 0.1 frames per second (FPS) and approximately1,000 FPS. For example, the lidar system 120A may generate point cloudsat a frame rate of approximately 0.1 FPS, 0.5 FPS, 1 FPS, 2 FPS, 5 FPS,10 FPS, 20 FPS, 100 FPS, 500 FPS, or 1,000 FPS. In an exampleimplementation, the lidar system 120A is configured to produce opticalpulses at a rate of 5×10⁵ pulses/second (e.g., the system may determine500,000 pixel distances per second) and scan a frame of 1000×50 pixels(e.g., 50,000 pixels/frame), which corresponds to a point-cloud framerate of 10 frames per second (e.g., 10 point clouds per second). Thepoint-cloud frame rate may be substantially fixed or dynamicallyadjustable, depending on the implementation. For example, the lidarsystem 120A may capture one or more point clouds at a particular framerate (e.g., 1 Hz) and then switch to capture one or more point clouds ata different frame rate (e.g., 10 Hz). In general, the lidar system canuse a slower frame rate (e.g., 1 Hz) to capture one or morehigh-resolution point clouds, and use a faster frame rate (e.g., 10 Hz)to rapidly capture multiple lower-resolution point clouds.

The field of regard of the lidar system 120A can overlap, encompass, orenclose at least a portion of the target 160, which may include all orpart of an object that is moving or stationary relative to lidar system120A. For example, the target 160 may include all or a portion of aperson, vehicle, motorcycle, truck, train, bicycle, wheelchair,pedestrian, animal, road sign, traffic light, lane marking, road-surfacemarking, parking space, pylon, guard rail, traffic barrier, pothole,railroad crossing, obstacle in or near a road, curb, stopped vehicle onor beside a road, utility pole, house, building, trash can, mailbox,tree, any other suitable object, or any suitable combination of all orpart of two or more objects.

With continued reference to FIG. 26A, the input beam 164A may passthrough the lens 170A which focuses the beam onto an active region 176Aof the receiver 128A. The active region 176A may refer to an area overwhich receiver 128A may receive or detect input light. The active region176A may have any suitable size or diameter d, such as for example, adiameter of approximately 25 μm, 50 μm, 80 μm, 100 μm, 200 μm, 500 μm, 1mm, 2 mm, or 5 mm. The overlap mirror 124A may have a reflecting surface174 that is substantially flat or the reflecting surface 174 may becurved (e.g., the mirror 124 may be an off-axis parabolic mirrorconfigured to focus the input beam 164 onto an active region of thereceiver 128A).

Next, FIG. 26B illustrates a lidar system 120B in which the lidar sensor10 discussed can be implemented. The lidar system 120B is generallysimilar to the lidar system 120A, but the lidar system 120B uses twoeyes to scan a combined FOR rather than a single eye. The scanner 11 inthis configuration uses two different reflective surfaces of the polygonmirror 12 to direct output beams 150A and 150B toward the target 160 andconcurrently receives and processes input beams 164A and 164B. Theoutput beams 150A and 150B are generated by different light sources 122Aand 122B, which can operate at a same wavelength or differentwavelength. In some implementations, the lidar system 120B is equippedwith two lasers, while in other implementations the light sources 122Aand 122B receive laser pulses from a shared laser inside or outside thehousing of the lidar system 120B.

Similar to the examples above, each of the output beams 150A and 150Bcan be further split to generate odd and even pixels, for example. Theinput beams 164A and 164B can follow different respective paths towardthe receivers 128A and 128B, respectively. More particularly, the inputbeam 164A can travel via an overlap mirror 124A toward a lens 170A,which focusses the light on the active region 176A of the receiver 128A,while the input beam 164B can travel via an overlap mirror 124B toward alens 170B, which focusses the light on the active region 176AB of thereceiver 128B. The lidar system 120B can provide a relatively largeangular separation between the outbound beams 150A and 150B, so as toreduce the probability of cross-talk detection.

The controller 130 in the configuration of FIG. 26B can receiveelectrical signals 145A and 145B from the receivers 128A and 128B,respectively, to determine one or more characteristics of the target160. The controller 130 can exchange control data with the light sources122A and 122B, the scanner 11, and the sensors 134.

FIG. 27 illustrates an example InGaAs avalanche photodiode (APD) 200.Referring back to FIGS. 26A and 26B, the receiver 128 may include one ormore APDs 200 configured to receive and detect light from input lightsuch as the beam 164A or 164B. More generally, the APD 200 can operatein any suitable receiver of input light. The APD 200 may be configuredto detect a portion of pulses of light which are scattered by a targetlocated downrange from the lidar system in which the APD 200 operates.For example, the APD 200 may receive a portion of a pulse of lightscattered by the target 160 depicted in FIGS. 26A and 26B, and generatean electrical-current signal corresponding to the received pulse oflight.

The APD 200 may include doped or undoped layers of any suitablesemiconductor material, such as for example, silicon, germanium, InGaAs,InGaAsP, or indium phosphide (InP). Additionally, the APD 200 mayinclude an upper electrode 202 and a lower electrode 206 for couplingthe ADP 200 to an electrical circuit. The APD 200 for example may beelectrically coupled to a voltage source that supplies a reverse-biasvoltage V to the APD 200. Additionally, the APD 200 may be electricallycoupled to a transimpedance amplifier which receives electrical currentgenerated by the APD 200 and produces an output voltage signal thatcorresponds to the received current. The upper electrode 202 or lowerelectrode 206 may include any suitable electrically conductive material,such as for example a metal (e.g., gold, copper, silver, or aluminum), atransparent conductive oxide (e.g., indium tin oxide), a carbon-nanotubematerial, or polysilicon. In some implementations, the upper electrode202 is partially transparent or has an opening to allow input light 210to pass through to the active region of the APD 200. In FIG. 27, theupper electrode 202 may have a ring shape that at least partiallysurrounds the active region of the APD 200, where the active regionrefers to an area over which the APD 200 may receive and detect theinput light 210. The active region may have any suitable size ordiameter d, such as for example, a diameter of approximately 25 μm, 50μm, 80 μm, 100 μm, 200 μm, 500 μm, 1 mm, 2 mm, or 5 mm.

The APD 200 may include any suitable combination of any suitablesemiconductor layers having any suitable doping (e.g., n-doped, p-doped,or intrinsic undoped material). In the example of FIG. 27, the InGaAsAPD 200 includes a p-doped InP layer 220, an InP avalanche layer 222, anabsorption layer 224 with n-doped InGaAs or InGaAsP, and an n-doped InPsubstrate layer 226. Depending on the implementation, the APD 200 mayinclude separate absorption and avalanche layers, or a single layer mayact as both an absorption and avalanche region. The APD 200 may operateelectrically as a PN diode or a PIN diode, and, during operation, theAPD 200 may be reverse-biased with a positive voltage V applied to thelower electrode 206 with respect to the upper electrode 202. The appliedreverse-bias voltage V may have any suitable value, such as for exampleapproximately 5 V, 10 V, 20 V, 30 V, 50 V, 75 V, 100 V, or 200 V.

In FIG. 27, photons of the input light 210 may be absorbed primarily inthe absorption layer 224, resulting in the generation of electron-holepairs (which may be referred to as photo-generated carriers). Forexample, the absorption layer 224 may be configured to absorb photonscorresponding to the operating wavelength of the lidar system 120A or120B (e.g., any suitable wavelength between approximately 1200 nm andapproximately 1600 nm). In the avalanche layer 222, anavalanche-multiplication process occurs where carriers (e.g., electronsor holes) generated in the absorption layer 224 collide with thesemiconductor lattice of the absorption layer 224, and produceadditional carriers through impact ionization. This avalanche processcan repeat numerous times so that one photo-generated carrier may resultin the generation of multiple carriers. As an example, a single photonabsorbed in the absorption layer 224 may lead to the generation ofapproximately 10, 50, 100, 200, 500, 1000, 10,000, or any other suitablenumber of carriers through an avalanche-multiplication process. Thecarriers generated in an APD 200 may produce an electrical current thatis coupled to an electrical circuit which may perform signalamplification, sampling, filtering, signal conditioning,analog-to-digital conversion, time-to-digital conversion, pulsedetection, threshold detection, rising-edge detection, or falling-edgedetection.

The number of carriers generated from a single photo-generated carriermay increase as the applied reverse bias V is increased. If the appliedreverse bias V is increased above a particular value referred to as theAPD breakdown voltage, then a single carrier can trigger aself-sustaining avalanche process (e.g., the output of the APD 200 issaturated regardless of the input light level). The APD 200 that isoperated at or above a breakdown voltage may be referred to as asingle-photon avalanche diode (SPAD) and may be referred to as operatingin a Geiger mode or a photon-counting mode. The APD 200 that is operatedbelow a breakdown voltage may be referred to as a linear APD, and theoutput current generated by the APD 200 may be sent to an amplifiercircuit (e.g., a transimpedance amplifier). The receiver 128A or 128B(see FIGS. 26A and 26B) may include an APD configured to operate as aSPAD and a quenching circuit configured to reduce a reverse-bias voltageapplied to the SPAD when an avalanche event occurs in the SPAD. The APD200 configured to operate as a SPAD may be coupled to an electronicquenching circuit that reduces the applied voltage V below the breakdownvoltage when an avalanche-detection event occurs. Reducing the appliedvoltage may halt the avalanche process, and the applied reverse-biasvoltage may then be re-set to await a subsequent avalanche event.Additionally, the APD 200 may be coupled to a circuit that generates anelectrical output pulse or edge when an avalanche event occurs.

In some implementations, the APD 200 or the APD 200 along withtransimpedance amplifier have a noise-equivalent power (NEP) that isless than or equal to 100 photons, 50 photons, 30 photons, 20 photons,or 10 photons. For example, the APD 200 may be operated as a SPAD andmay have a NEP of less than or equal to 20 photons. As another example,the APD 200 may be coupled to a transimpedance amplifier that producesan output voltage signal with a NEP of less than or equal to 50 photons.The NEP of the APD 200 is a metric that quantifies the sensitivity ofthe APD 200 in terms of a minimum signal (or a minimum number ofphotons) that the APD 200 can detect. The NEP may correspond to anoptical power (or to a number of photons) that results in asignal-to-noise ratio of 1, or the NEP may represent a threshold numberof photons above which an optical signal may be detected. For example,if the APD 200 has a NEP of 20 photons, then an input beam with 20photons may be detected with a signal-to-noise ratio of approximately 1(e.g., the APD 200 may receive 20 photons from the input beam 210 andgenerate an electrical signal representing the input beam 210 that has asignal-to-noise ratio of approximately 1). Similarly, an input beam with100 photons may be detected with a signal-to-noise ratio ofapproximately 5. In some implementations, the lidar system 120A or 120Bwith the APD 200 (or a combination of the APD 200 and transimpedanceamplifier) having a NEP of less than or equal to 100 photons, 50photons, 30 photons, 20 photons, or 10 photons offers improved detectionsensitivity with respect to a conventional lidar system that uses a PNor PIN photodiode. For example, an InGaAs PIN photodiode used in aconventional lidar system may have a NEP of approximately 10⁴ to 10⁵photons, and the noise level in a lidar system with an InGaAs PINphotodiode may be 10³ to 10⁴ times greater than the noise level in alidar system 120A or 120B with the InGaAs APD detector 200.

Referring back to FIGS. 26A and 26B, an optical filter may be located infront of the receiver 128A or 128B and configured to transmit light atone or more operating wavelengths of the light source 122A or 122B andattenuate light at surrounding wavelengths. For example, an opticalfilter may be a free-space spectral filter located in front of APD 200of FIG. 27. This spectral filter may transmit light at the operatingwavelength of the light source 122A or 122B (e.g., between approximately1530 nm and 1560 nm) and attenuate light outside that wavelength range.As a more specific example, light with wavelengths of approximately200-1530 nm or 1560-2000 nm may be attenuated by any suitable amount,such as for example, by at least 5 dB, 10 dB, 20 dB, 30 dB, or 40 dB.

Next, FIG. 28 illustrates an APD 250 coupled to an examplepulse-detection circuit 254. The APD 250 can be similar to the APD 200discussed above, or can be any other suitable detector. Thepulse-detection circuit 254 can operate in the lidar system of FIG. 26Aor 26B as part of the receiver 128. Further, the pulse-detection circuit254 can operate in the receiver 128 of FIG. 26A, the receiver 128A ofFIG. 26B, or any other suitable receiver. The pulse-detection circuit254 alternatively can be implemented in the controller 130 or anothersuitable controller. In some implementations, parts of thepulse-detection circuit 254 can operate in a receiver and other parts ofthe pulse-detection circuit 254 can operate in a controller. Forexample, components 256 and 258 may be a part of the receiver 140, andcomponents 260 and 262 may be a part of the controller 130.

The pulse-detection circuit 254 may include circuitry that receives asignal from a detector (e.g., an electrical current from the APD 250)and performs current-to-voltage conversion, signal amplification,sampling, filtering, signal conditioning, analog-to-digital conversion,time-to-digital conversion, pulse detection, threshold detection,rising-edge detection, or falling-edge detection. The pulse-detectioncircuit 254 may determine whether an optical pulse has been received bythe APD 250 or may determine a time associated with receipt of anoptical pulse by the APD 250. Additionally, the pulse-detection circuit254 may determine a duration of a received optical pulse. In an exampleimplementation, the pulse-detection circuit 254 includes atransimpedance amplifier (TIA) 256, a gain circuit 258, a comparator260, and a time-to-digital converter (TDC) 262.

The TIA 256 may be configured to receive an electrical-current signalfrom the APD 250 and produce a voltage signal that corresponds to thereceived electrical-current signal. For example, in response to areceived optical pulse, the APD 250 may produce a current pulsecorresponding to the optical pulse. The TIA 256 may receive the currentpulse from the APD 250 and produce a voltage pulse that corresponds tothe received current pulse. The TIA 256 may also act as an electronicfilter. For example, the TIA 256 may be configured as a low-pass filterthat removes or attenuates high-frequency electrical noise byattenuating signals above a particular frequency (e.g., above 1 MHz, 10MHz, 20 MHz, 50 MHz, 100 MHz, 200 MHz, or any other suitable frequency).

The gain circuit 258 may be configured to amplify a voltage signal. Asan example, the gain circuit 258 may include one or morevoltage-amplification stages that amplify a voltage signal received fromthe TIA 256. For example, the gain circuit 258 may receive a voltagepulse from the TIA 256, and the gain circuit 258 may amplify the voltagepulse by any suitable amount, such as for example, by a gain ofapproximately 3 dB, 10 dB, 20 dB, 30 dB, 40 dB, or 50 dB. Additionally,the gain circuit 258 may also act as an electronic filter configured toremove or attenuate electrical noise.

The comparator 260 may be configured to receive a voltage signal fromthe TIA 256 or the gain circuit 258 and produce an electrical-edgesignal (e.g., a rising edge or a falling edge) when the received voltagesignal rises above or falls below a particular threshold voltage VT. Asan example, when a received voltage rises above VT, the comparator 260may produce a rising-edge digital-voltage signal (e.g., a signal thatsteps from approximately 0 V to approximately 2.5 V, 3.3 V, 5 V, or anyother suitable digital-high level). As another example, when a receivedvoltage falls below VT, the comparator 260 may produce a falling-edgedigital-voltage signal (e.g., a signal that steps down fromapproximately 2.5 V, 3.3 V, 5 V, or any other suitable digital-highlevel to approximately 0 V). The voltage signal received by thecomparator 260 may be received from the TIA 256 or the gain circuit 258and may correspond to an electrical-current signal generated by the APD250. For example, the voltage signal received by the comparator 260 mayinclude a voltage pulse that corresponds to an electrical-current pulseproduced by the APD 250 in response to receiving an optical pulse. Thevoltage signal received by the comparator 260 may be an analog signal,and an electrical-edge signal produced by the comparator 260 may be adigital signal.

The time-to-digital converter (TDC) 262 may be configured to receive anelectrical-edge signal from the comparator 260 and determine an intervalof time between emission of a pulse of light by the light source andreceipt of the electrical-edge signal. The output of the TDC 262 may bea numerical value that corresponds to the time interval determined bythe TDC 262. In some implementations, the TDC 262 has an internalcounter or clock with any suitable period, such as for example, 5 ps, 10ps, 15 ps, 20 ps, 30 ps, 50 ps, 100 ps, 0.5 ns, 1 ns, 2 ns, 5 ns, or 10ns. The TDC 262 for example may have an internal counter or clock with a20 ps period, and the TDC 262 may determine that an interval of timebetween emission and receipt of a pulse is equal to 25,000 time periods,which corresponds to a time interval of approximately 0.5 microseconds.The TDC 262 may send the numerical value “25000” to a processor orcontroller 130 of the lidar system 120A or 120B, which may include aprocessor configured to determine a distance from the lidar system 120Aor 120B to the target 160 based at least in part on an interval of timedetermined by a TDC 262. The processor may receive a numerical value(e.g., “25000”) from the TDC 262 and, based on the received value, theprocessor may determine the distance from the lidar system 120A or 120Bto the target 160.

IV. Placement and Operation of a Lidar Sensor Unit in a Vehicle

Depending on where a lidar sensor unit is mounted on a vehicle, one ormore of the surfaces of the housing could coincide with an external orinterior surface of a vehicle. Example surfaces include a hood, aquarter-panel, a sideview mirror housing, a trunk lid, grill, headlampor tail light housing, dashboard, vehicle roof, front bumper, rearbumper, or other vehicle body part surface. When provided in avulnerable location of a vehicle, such as a front or rear bumper, thefront or rear bumper may be fortified or reinforced with additionalforce resistance or force dampening features to protect sensitivecomponents of the lidar sensor unit 10 from damage. The low profile ofthe lidar sensor unit 10 lends itself to being strategically located atoptimal locations of a vehicle body without detracting from theaesthetic appearance of the vehicle. For example, a plurality of thelidar sensor units 10 may be disposed one at each front corner, or evenone at each of all four corners, of a vehicle roof, with the majority ofthe volume occupied by the lidar sensor units 10 embedded within theroof, so that only a window of the unit protrudes prominently of thevehicle roof (or other vehicle surface in which the lidar sensor unit 10is embedded).

The components of the lidar sensor unit 10 may be configured so that atleast a portion of the planar mirror 14 extends above the rotatablepolygon mirror 12, and only a region extending from a lower edge of theplanar mirror 14 to a top of the housing projects prominently from asurface of a body of a vehicle on which the lidar sensor unit 10 isdeployed.

More particularly, as illustrated in FIG. 29, a housing 302 may enclosea lidar sensor unit. Some or all of the enclosed components can be thecomponents of the lidar sensor unit 10. The housing 302 is placed in anopening in a surface 300, which may correspond to a section of a vehicleroof or another suitable surface of a vehicle. A portion 306 protrudesprominently above the surface 300, and a portion is 304 is “submerged”under the surface 300. The portion 306 includes a window 308 throughwhich input and output beams of light travel. The size of the submergedportion of 304 is larger than the protruding portion 306, in at leastsome of the implementations, to reduce aerodynamic drag. Although thewindow 308 is illustrated in FIG. 29 as a vertical surface perpendicularto the surface 300, in general the window 308 may be sloped, curved, orotherwise configured to direct a flow of air around the protrudingportion 306. In an example implementation, the size of the window 308corresponds approximately to the size of the planar mirror 14. Thewindow 308 may be the same or similar to the window 167 depicted inFIGS. 26A and 26B.

Referring to FIG. 30, the housing 302 may be embedded in the roof of avehicle 320, with the window 308 oriented similar to the windshield ofthe vehicle 320. The housing 302 encloses the lidar sensor unit 10,oriented so that the axis of rotation 324 of the polygon mirror 12 isaligned with a longitudinal axis of the vehicle 326. This orientationmay serve to reduce adverse effects of vibration, acceleration, anddeceleration. Thus, when the vehicle 320 accelerates quickly, thepolygon mirror enclosed in the housing 302 may be displaced along theaxis 324, and the input and output beams impinge on the surface of thepolygon mirror on the same plane as in the configuration prior to thedisplacement, which does not result in the scan lines being misalignedto displaced (i.e., the beams may strike different portions of thereflective surface, but the reflection imparted by these portions of thereflective surface is the same as in the original configuration).Similarly, when the vehicle 320 decelerates quickly, the potentialdisplacement of the polygon mirror along the axis 324 does not adverselyaffect the scan lines. In contrast to these scenarios, when axis 324 isperpendicular to the orientation of the vehicle 320, the displacement ofthe polygon mirror may result in the FOR_(H) shifting right or left,which in turn results in scan errors.

In general, any suitable number of lidar sensor units 10 may beintegrated into a vehicle. In one example implementation, multiple lidarsensor units 10, operating in a lidar system similar to the system 120B,may be integrated into a car to provide a complete 360-degree horizontalFOR around the car. As another example, 4-10 lidar sensor units 10, eachsystem having a 45-degree to 90-degree horizontal FOR, may be combinedtogether to form a sensing system that provides a point cloud covering a360-degree horizontal FOR. The lidar sensor units 10 may be oriented sothat adjacent FORs have an amount of spatial or angular overlap to allowdata from the multiple lidar sensor units 10 to be combined or stitchedtogether to form a single or continuous 360-degree point cloud. As anexample, the FOR of each lidar sensor unit 10 may have approximately1-15 degrees of overlap with an adjacent FOR. In particular embodiments,a vehicle may refer to a mobile machine configured to transport peopleor cargo. For example, a vehicle may include, may take the form of, ormay be referred to as a car, automobile, motor vehicle, truck, bus, van,trailer, off-road vehicle, farm vehicle, lawn mower, constructionequipment, golf cart, motorhome, taxi, motorcycle, scooter, bicycle,skateboard, train, snowmobile, watercraft (e.g., a ship or boat),aircraft (e.g., a fixed-wing aircraft, helicopter, or dirigible), orspacecraft. In particular embodiments, a vehicle may include an internalcombustion engine or an electric motor that provides propulsion for thevehicle.

Referring to FIG. 31, lidar sensor units 322A-D are installed in theroof of a vehicle 320, in an example implementation. Each of the lidarsensor units 322A-D is approximately at 45° relative to one of the edgesof the roof. The lidar sensor units 322A-D thus are oriented so that theFOR of the lidar sensor unit 322A covers an area in front of the vehicleand to the right of the vehicle, the FOR of the lidar sensor unit 322Bcovers an area behind the vehicle and to the right of the vehicle, theFOR of the lidar sensor unit 322C covers an area behind the vehicle andto the left of the vehicle, and the FOR of the lidar sensor unit 322Dcovers an area in front of the vehicle and to the left of the vehicle.The FORs of the lidar sensor units 322A and 322D have an angular overlap(e.g., five degrees) directly in front of the vehicle, in an exampleimplementation. Further, in an example implementation, the FORs of thelidar sensor units 322A and 322B have no angular overlap or littleangular overlap.

In some implementations, one or more lidar sensor units 10 are includedin a vehicle as part of an advanced driver assistance system (ADAS) toassist a driver of the vehicle in the driving process. For example, alidar sensor units 10 may be part of an ADAS that provides informationor feedback to a driver (e.g., to alert the driver to potential problemsor hazards) or that automatically takes control of part of a vehicle(e.g., a braking system or a steering system) to avoid collisions oraccidents. The lidar sensor units 10 may be part of a vehicle ADAS thatprovides adaptive cruise control, automated braking, automated parking,collision avoidance, alerts the driver to hazards or other vehicles,maintains the vehicle in the correct lane, or provides a warning if anobject or another vehicle is in a blind spot.

In some cases, one or more lidar sensor units 10 are integrated into avehicle as part of an autonomous-vehicle driving system. In an exampleimplementation, the lidar sensor units 10 provides information about thesurrounding environment to a driving system of an autonomous vehicle. Anautonomous-vehicle driving system may include one or more computingsystems that receive information from the lidar sensor units 10 aboutthe surrounding environment, analyze the received information, andprovide control signals to the vehicle's driving systems (e.g., steeringwheel, accelerator, brake, or turn signal). For example, the lidarsensor units 10 integrated into an autonomous vehicle may provide anautonomous-vehicle driving system with a point cloud every 0.1 seconds(e.g., the point cloud has a 10 Hz update rate, representing 10 framesper second). The autonomous-vehicle driving system may analyze thereceived point clouds to sense or identify targets 160 (see FIGS. 26Aand 26B) and their respective locations, distances, or speeds, and theautonomous-vehicle driving system may update control signals based onthis information. As an example, if the lidar sensor unit 10 detects avehicle ahead that is slowing down or stopping, the autonomous-vehicledriving system may send instructions to release the accelerator andapply the brakes.

An autonomous vehicle may be referred to as an autonomous car,driverless car, self-driving car, robotic car, or unmanned vehicle. Anautonomous vehicle may be a vehicle configured to sense its environmentand navigate or drive with little or no human input. For example, anautonomous vehicle may be configured to drive to any suitable locationand control or perform all safety-critical functions (e.g., driving,steering, braking, parking) for the entire trip, with the driver notexpected to control the vehicle at any time. As another example, anautonomous vehicle may allow a driver to safely turn their attentionaway from driving tasks in particular environments (e.g., on freeways),or an autonomous vehicle may provide control of a vehicle in all but afew environments, requiring little or no input or attention from thedriver.

An autonomous vehicle may be configured to drive with a driver presentin the vehicle, or an autonomous vehicle may be configured to operatethe vehicle with no driver present. As an example, an autonomous vehiclemay include a driver's seat with associated controls (e.g., steeringwheel, accelerator pedal, and brake pedal), and the vehicle may beconfigured to drive with no one seated in the driver's seat or withlittle or no input from a person seated in the driver's seat. As anotherexample, an autonomous vehicle may not include any driver's seat orassociated driver's controls, and the vehicle may perform substantiallyall driving functions (e.g., driving, steering, braking, parking, andnavigating) without human input. As another example, an autonomousvehicle may be configured to operate without a driver (e.g., the vehiclemay be configured to transport human passengers or cargo without adriver present in the vehicle). As another example, an autonomousvehicle may be configured to operate without any human passengers (e.g.,the vehicle may be configured for transportation of cargo without havingany human passengers onboard the vehicle).

As indicated above, a light source of the lidar sensor unit 10 can belocated remotely from some of the other components of the lidar sensorunit 10 (such as the scanner 11 and the receiver 128A or 128B).Moreover, a lidar system implemented in a vehicle may include fewerlight sources than scanners and receivers.

FIG. 32 illustrates an example vehicle 350 with a lidar system 351 thatincludes a laser 353 with multiple sensor heads 352 coupled to the laser353 via multiple laser-sensor links 370. Each of the sensor heads 352can be implemented similar to the lidar sensor unit 10.

Each of the laser-sensor links 370 may include one or more optical linksand/or one or more electrical links. The sensor heads 352 in FIG. 32 arepositioned or oriented to provide a greater than 30-degree view of anenvironment around the vehicle. More generally, a lidar system withmultiple sensor heads may provide a horizontal field of regard around avehicle of approximately 30°, 45°, 60°, 90°, 120°, 180°, 270°, or 360°.Each of the sensor heads 352 may be attached to or incorporated into abumper, fender, grill, side panel, spoiler, roof, headlight assembly,taillight assembly, rear-view mirror assembly, hood, trunk, window, orany other suitable part of the vehicle.

In the example of FIG. 32, four sensor heads 352 are positioned at ornear the four corners of the roof of the vehicle, and the laser 353 maybe located within the vehicle (e.g., in or near the trunk). The foursensor heads 352 may each provide a 90° to 120° horizontal field ofregard (FOR), and the four sensor heads 352 may be oriented so thattogether they provide a complete 360-degree view around the vehicle. Asanother example, the lidar system 351 may include six sensor heads 352positioned on or around a vehicle, where each of the sensor heads 352provides a 60° to 90° horizontal FOR. As another example, the lidarsystem 351 may include eight sensor heads 352, and each of the sensorheads 352 may provide a 45° to 60° horizontal FOR. As yet anotherexample, the lidar system 351 may include six sensor heads 352, whereeach of the sensor heads 352 provides a 70° horizontal FOR with anoverlap between adjacent FORs of approximately 10°. As another example,the lidar system 351 may include two sensor heads 352 which togetherprovide a forward-facing horizontal FOR of greater than or equal to300°.

Data from each of the sensor heads 352 may be combined or stitchedtogether to generate a point cloud that covers a greater than or equalto 30-degree horizontal view around a vehicle. For example, the laser353 may include a controller or processor that receives data from eachof the sensor heads 352 (e.g., via a corresponding electrical link 370)and processes the received data to construct a point cloud covering a360-degree horizontal view around a vehicle or to determine distances toone or more targets. The point cloud or information from the point cloudmay be provided to a vehicle controller 372 via a correspondingelectrical, optical, or radio link 370. In some implementations, thepoint cloud is generated by combining data from each of the multiplesensor heads 352 at a controller included within the laser 353 andprovided to the vehicle controller 372. In other implementations, eachof the sensor heads 352 includes a controller or process that constructsa point cloud for a portion of the 360-degree horizontal view around thevehicle and provides the respective point cloud to the vehiclecontroller 372. The vehicle controller 372 then combines or stitchestogether the points clouds from the respective sensor heads 352 toconstruct a combined point cloud covering a 360-degree horizontal view.Still further, the vehicle controller 372 in some implementationscommunicates with a remote server to process point cloud data.

In any event, the vehicle 350 may be an autonomous vehicle where thevehicle controller 372 provides control signals to various components390 within the vehicle 350 to maneuver and otherwise control operationof the vehicle 350. The components 390 are depicted in an expanded viewin FIG. 32 for ease of illustration only. The components 390 may includean accelerator 374, brakes 376, a vehicle engine 378, a steeringmechanism 380, lights 382 such as brake lights, head lights, reverselights, emergency lights, etc., a gear selector 384, and/or othersuitable components that effectuate and control movement of the vehicle350. The gear selector 384 may include the park, reverse, neutral, drivegears, etc. Each of the components 390 may include an interface viawhich the component receives commands from the vehicle controller 372such as “increase speed,” “decrease speed,” “turn left 5 degrees,”“activate left turn signal,” etc. and, in some cases, provides feedbackto the vehicle controller 372.

In some implementations, the vehicle controller 372 receives point clouddata from the sensor heads 352 via the link 373 and analyzes thereceived point cloud data to sense or identify targets 130 and theirrespective locations, distances, speeds, shapes, sizes, type of target(e.g., vehicle, human, tree, animal), etc. The vehicle controller 372then provides control signals via the link 373 to the components 390 tocontrol operation of the vehicle based on the analyzed information. Forexample, the vehicle controller 372 may identify an intersection basedon the point cloud data and determine that the intersection is theappropriate location at which to make a left turn. Accordingly, thevehicle controller 372 may provide control signals to the steeringmechanism 380, the accelerator 374, and brakes 376 for making a properleft turn. In another example, the vehicle controller 372 may identify atraffic light based on the point cloud data and determine that thevehicle 350 needs to come to a stop. As a result, the vehicle controller372 may provide control signals to release the accelerator 374 and applythe brakes 376.

As another example, FIG. 33 illustrates a vehicle 400 in which a laser404 is optically coupled to six sensor heads 402, each of which can beimplemented as the lidar sensor unit 10. The sensor heads 402A and 402Gare disposed at the front of the vehicle 400, the sensor heads 402B and402F are disposed in the side view mirrors, and the sensor heads 402C-Eare disposed on the trunk. In particular, the sensor head 402D isoriented to face backward relative to the orientation of the vehicle400, and the sensor heads 402E and 402C are oriented at approximately 45degrees relative to the axis of orientation of the sensor head 402D.

V. Manufacturing a Highly Balanced Polygon Mirror

The reflective surfaces 18-24 of the polygon mirror 12 may bemanufactured using surface replication techniques. Coarse and finebalancing techniques, including (by way of example only) the use ofdrilling, milling, etching, and polishing, can be employed prior tomounting the polygon mirror 12 to a motor 32, and subsequent tomounting, high-energy laser pulses can be utilized to remove matter atprecise locations on the polygon mirror 12. The coarse balancingtechniques employed may include utilizing a shaft-balancing machine.Further, in forming the block 16, a hollowed-out substrate may be usedto reduce the weight of the block.

More particularly, FIG. 34 depicts a flow diagram of an example method500 for manufacturing a highly balanced rotatable polygon mirror thatcan be used as the polygon mirror 12 in the lidar sensor unit 10.

First, a block for a polygon mirror is formed (502). A glass substrateis used in an example implementation. In general, any suitable materialsuch as a plastic, a polycarbonate, a composite material, metal, carbonfiber, or a ceramic can be used. It is also possible to use a metalframe with inserts of material susceptible to ablation by high-poweredlasers. For example, a metal frame can contain glass or plasticcylinders at or near the corners of the block.

Next, a coarse balancing procedure is used (504) to obtain a relativelybalanced block. The coarse balancing procedure can involve one or moreof drilling, milling, etching, polishing, or any other suitabletechnique. Balancing machines available today from various manufacturerscan be used during coarse balancing. However, many balancing machines,even small-part balancing machines, cannot provide precise balancingdesirable in the lidar sensor unit 10. Small deviations in weightdistribution can result in non-uniform angular velocity when the polygonmirror 12 rotates at a high rate, which in turn can result in distortionof scan lines (e.g., wrong distances between adjacent pixels).

Further, one or more surfaces of the block formed at block 502 can bemade reflective (506). Referring to FIGS. 10-12, for example, all foursurfaces of the polygon mirror block 12 can be made reflective, but inother implementations of the scanner only one of the surfaces can bemade reflective, or two non-adjacent surfaces can be made reflective. Inone implementation of the method 500, the one or more surfaces of theblock are made reflective using surface replication, e.g., by creating athin reflective film and applying the film to the surfaces of the block.Surface replication can be applied to two opposite sides of the block atthe same time to accelerate the process of manufacturing a highlybalanced mirror. Other coating (e.g., sputtering) and non-coatingtechniques also can be used to make the surfaces reflective, preferablythose techniques that reduce the probability of damaging the reflectivesurfaces during the fine balancing procedure. In some implementations,the order of execution of procedures 504 and 506 can be reversed (i.e.,coarse balancing can occur before making the surfaces reflective orafter making the surfaces reflective).

Once the block acquires one or more reflective surfaces and isapproximately balanced, the block is mated to a motor (508). To reducethe probability of subsequently damaging a precisely balanced block, theblock is mated to the motor in the corresponding assembly of the lidarsensor unit 10. As a more specific example, the polygon mirror axle 30is inserted through or attached to a coarsely balanced polygon mirror12, and the coarsely balanced polygon mirror 12 is installed on thebracket 29 and mated to the motor 32 (see FIGS. 1 and 2). After thepolygon mirror 12 is precisely balanced as discussed below, the assemblyincluding the components 12, 29, 30, and 32 is used in the lidar sensorunit 10 as a single unit, i.e., is not disassembled into the individualcomponents.

To balance the block more precisely, rotation is imparted to the block(510) and material is removed from the block using high-energy laserpulses or a continuous laser beam (512). The removal of the material canbe optimized by selecting a laser having an appropriate operatingwavelength based on the material from which the block is made. Forexample, a laser operating in the ultraviolet wavelength range (e.g., anexcimer laser) may be used to ablate material from a block made of glassor plastic. As another example, a laser operating in the infraredwavelength range (e.g., a neodymium-doped yttrium-aluminum-garnet(Nd:YAG) laser operating at a wavelength of approximately 1.06 μm or aCO₂ laser operating at 9.4-10.6 μm) may be used to ablate material froma block made of metal. To continue with the example above, the motor 32can impart rotation to the polygon mirror 12, and a high-power laser canaim at the wall 26 (best illustrated in FIGS. 2 and 3). The laser can beaimed at the regions close to the corners, where the impact on angularvelocity due to torque is the greatest, due to the vertical orientationof the polygon mirror 12. In some implementations, material may beremoved from the axle or shaft attached to the polygon mirror 12 andabout which the polygon mirror 12 rotates.

As the block rotates and ablation is carried out, the changes inbalancing can be monitored by, for example, determining rotational speedof the block and determining the differences between the speed ofindividual facets. To this end, a stationary photo-interrupter can beused, with tabs corresponding to each facet provided on the axis ofrotation of the block (or on the block itself). As the tabs pass throughthe stationary photo-interrupter, the rate each facet is traveling canbe measured. Thus, if for a block with four facets, the time between thefirst tab and the second tab traveling past the photo-interrupter is t,the time between the second tab and the third tab traveling past thephoto-interrupter is t+e, the time between the third tab and the fourthtab traveling past the photo-interrupter is t+e′, and the time betweenthe third tab and the fourth tab traveling past the photo-interrupter ist+e″. Ablation can be applied to the block so as to make thesemeasurements as close to each other as practically possible. After theprocedure of rotation and material removal (510,512) is completed, thetime between each pair of adjacent tab traveling past thephoto-interrupter is as close to t as possible. A controller, aworkstation, or any suitable computing device can be used to control thehigh-powered laser used in ablation in view of the data from thephoto-interrupter. The controller also can determine the changes in timebetween pairs of adjacent tabs traveling past the photo-interrupter andgenerate an appropriate notification for the operator to indicate whenthe process is complete, or automatically complete the method 500,depending on the implementation.

In another implementation, a light source (not necessarily a laser) canbe used to direct a light at the block, with a temporary detector beingin a fixed position relative to the block, so as to determine the rateat which each facet is moving. The light source can direct a beam oflight at the block, which reflects the beam of light along a scan line.The temporary detector can be placed at a point on the scan line, in thepath of the beam of light. The controller can measure the times at whichthe temporary detector detects the beam of light and derive theappropriate measurements of t+e, t+e′, etc., similar to the exampleabove. Similar to the example above, the controller then canautomatically shut down the laser emitting high-energy pulses and/orprovide a notification to the operator.

In yet another implementation, a balancing machine can be used alongwith a high-energy laser for the fine-balancing process.

In some implementations, all or part of a method for manufacturing ahighly balanced rotatable polygon mirror as described herein may beapplied to any suitable rotating object. For example, material removalby a laser source to form a high-balanced rotatable object may beapplied to a high-speed motor, dental drill, or hard disk drive.

VI. Scan Patterns and Scan Pattern Modifications in a Lidar Sensor Unit

FIG. 35 illustrates an example light-source field of view (FOV_(L)) andreceiver field of view (FOV_(R)) for the lidar sensor unit 10 and/or thelidar system 120A or 120B, as well as a scan pattern 520 which the lidarsensor unit 10 and/or the lidar system 120 can produce.

The scan pattern 520 corresponds to a scan across any suitable field ofregard (FOR) having any suitable horizontal FOR (FOR_(H)) and anysuitable vertical FOR (FOR_(V)). For example, a certain scan pattern mayhave a field of regard represented by angular dimensions (e.g.,FOR_(H)×FOR_(V)) 40°×30°, 90°×40°, or 60°×15°. As another example, acertain scan pattern may have a FOR_(H) greater than or equal to 10°,25°, 30°, 40°, 60°, 90°, or 120°. As yet another example, a certain scanpattern may have a FOR_(V) greater than or equal to 2°, 5°, 10°, 15°,20°, 30°, or 45°. In the example of FIG. 35, a reference line 522represents a center of the field of regard of the scan pattern 520. Thereference line 522 may have any suitable orientation, such as, ahorizontal angle of 0° (e.g., reference line 522 may be orientedstraight ahead) and a vertical angle of 0° (e.g., reference line 522 mayhave an inclination of 0°), or the reference line 522 may have a nonzerohorizontal angle or a nonzero inclination (e.g., a vertical angle of+10° or −10°). In FIG. 35, if the scan pattern 520 has a 60×15° field ofregard, then the scan pattern 520 covers a ±30° horizontal range withrespect to reference line 522 and a ±7.5° vertical range with respect toreference line 522. Additionally, an optical beam 532 in FIG. 35 has anorientation of approximately −15° horizontal and +3° vertical withrespect to reference line 522. The beam 532 may be referred to as havingan azimuth of −15° and an altitude of +3° relative to the reference line246. An azimuth (which may be referred to as an azimuth angle) mayrepresent a horizontal angle with respect to the reference line 522, andan altitude (which may be referred to as an altitude angle, elevation,or elevation angle) may represent a vertical angle with respect to thereference line 522.

The scan pattern 520 may include multiple pixels along scan lines 524,each pixel corresponding to instantaneous light-source FOV_(L). Eachpixel may be associated with one or more laser pulses and one or morecorresponding distance measurements. A cycle of the scan pattern 520 mayinclude a total of P_(x)×P_(y) pixels (e.g., a two-dimensionaldistribution of P_(x) by P_(y) pixels). For example, the scan pattern520 may include a distribution with dimensions of approximately100-2,000 pixels along a horizontal direction and approximately 4-200pixels along a vertical direction. As another example, the scan pattern520 may include a distribution of 1,000 pixels along the horizontaldirection by 64 pixels along the vertical direction (e.g., the framesize is 1000×64 pixels) for a total of 64,000 pixels per cycle of scanpattern 520. The number of pixels along a horizontal direction may bereferred to as a horizontal resolution of the scan pattern 520, and thenumber of pixels along a vertical direction may be referred to as avertical resolution of the scan pattern 520. As an example, the scanpattern 520 may have a horizontal resolution of greater than or equal to100 pixels and a vertical resolution of greater than or equal to 4pixels. As another example, the scan pattern 520 may have a horizontalresolution of 100-2,000 pixels and a vertical resolution of 4-400pixels.

Each pixel may be associated with a distance (e.g., a distance to aportion of a target 160 from which the corresponding laser pulse wasscattered) or one or more angular values. As an example, the pixel maybe associated with a distance value and two angular values (e.g., anazimuth and altitude) that represent the angular location of the pixelwith respect to the lidar system 120A or 120B. A distance to a portionof the target 160 may be determined based at least in part on atime-of-flight measurement for a corresponding pulse. An angular value(e.g., an azimuth or altitude) may correspond to an angle (e.g.,relative to reference line 522) of the output beam 532 (e.g., when acorresponding pulse is emitted from the lidar sensor unit 10 or thelidar system 120) or an angle of the input beam 534 (e.g., when an inputsignal is received by the lidar sensor unit 10 or the lidar system 120Aor 120B). In some implementations, the lidar sensor unit 10 or the lidarsystem 120A or 120B determines an angular value based at least in parton a position of a component of the scanner 11. For example, an azimuthor altitude value associated with the pixel may be determined from anangular position of one or more corresponding scanning mirrors of thescanner 11.

The light source 122A or 122B may emit pulses of light as the FOV_(L)and FOV_(R) are scanned by the scanner 11 across the FOR. Thelight-source field of view may refer to an angular cone illuminated bythe light source 122A or 122B at a particular instant of time or anangular cone that would be illuminated by the light source 122A or 122Bat a particular instant of time if the light source 122A or 122B were toemit light at that instant of time. For example, when the light source122A or 122B operates in a pulsed mode, the light source 122A or 122Bmay continuously change its orientation relative to the external worldbut actively illuminate corresponding regions only during the dutycycle.

Similarly, a receiver field of view may refer to an angular cone overwhich the receiver 128A or 128B may receive or detect light at aparticular instant of time, and any light outside the receiver field ofview may not be received or detected. For example, as the scanner 11scans the light-source field of view across a field of regard, the lidarsensor unit 10 or the lidar system 120A or 120B may send the pulse oflight in the direction the FOV_(L) is pointing at the time the lightsource 122A or 122B emits the pulse. The pulse of light may scatter offthe target 160, and the receiver 128A or 128B may receive and detect aportion of the scattered light that is directed along or containedwithin the FOV_(R).

An instantaneous FOV may refer to an angular cone being illuminated by apulse directed along the direction the light-source FOV is pointing atthe instant the pulse of light is emitted. Thus, while the light-sourceFOV and the detector FOV are scanned together in a synchronous manner(e.g., the scanner 11 scans both the light-source FOV and the detectorFOV across the field of regard along the same scan direction and at thesame scan speed, maintaining the same relative position to each other),the instantaneous FOV remains “stationary,” and the detector FOVeffectively moves relative to the instantaneous FOV. More particularly,when a pulse of light is emitted, the scanner 11 directs the pulse alongthe direction in which the light-source FOV currently is pointing. Eachinstantaneous FOV (IFOV) corresponds to a pixel. Thus, each time a pulseis emitted, the lidar sensor unit 10 or the lidar system 120A or 120Bproduces or defines an IFOV (or pixel) that is fixed in place andcorresponds to the light-source FOV at the time when the pulse isemitted. During operation of the scanner 11, the detector FOV movesrelative to the light-source IFOV but does not move relative to thelight-source FOV.

In some implementations, the scanner 11 is configured to scan both alight-source field of view and a receiver field of view across a fieldof regard of the lidar system 120A or 120B. The lidar system 120A or120B may emit and detect multiple pulses of light as the scanner 11scans the FOV_(L) and FOV_(R) across the field of regard while tracingout the scan pattern 520. The scanner 11 in some implementations scansthe light-source field of view and the receiver field of viewsynchronously with respect to one another. In this case, as the scanner11 scans FOV_(L) across a scan pattern 520, the FOV_(R) followssubstantially the same path at the same scanning speed. Additionally,the FOV_(L) and FOV_(R) may maintain the same relative position to oneanother as the scanner 11 scans FOV_(L) and FOV_(R) across the field ofregard. For example, the FOV_(L) may be substantially overlapped with orcentered inside the FOV_(R), and the scanner 11 may maintain thisrelative positioning between FOV_(L) and FOV_(R) throughout a scan. Asanother example, the FOV_(R) may lag behind the FOV_(L) by a particular,fixed amount throughout a scan (e.g., the FOV_(R) may be offset from theFOV_(L) in a direction opposite the scan direction). As yet anotherexample, during a time between the instant when a pulse is emitted andprior to the time when the pulse can return from a target located at themaximum distance R_(MAX), FOV_(R) may move relative to the IFOV or pixelto define different amounts of overlap, as discussed in more detailbelow.

The FOV_(L) may have an angular size or extent Θ_(L) that issubstantially the same as or that corresponds to the divergence of theoutput beam 532, and the FOV_(R) may have an angular size or extentΘ_(R) that corresponds to an angle over which the receiver 128 mayreceive and detect light. The receiver field of view may be any suitablesize relative to the light-source field of view. For example, thereceiver field of view may be smaller than, substantially the same sizeas, or larger than the angular extent of the light-source field of view.In some implementations, the light-source field of view has an angularextent of less than or equal to 50 milliradians, and the receiver fieldof view has an angular extent of less than or equal to 50 milliradians.The FOV_(L) may have any suitable angular extent Θ_(L), such as forexample, approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2mrad, 3 mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Similarly,the FOV_(R) may have any suitable angular extent Θ_(R), such as forexample, approximately 0.1 mrad, 0.2 mrad, 0.5 mrad, 1 mrad, 1.5 mrad, 2mrad, 3 mrad, 5 mrad, 10 mrad, 20 mrad, 40 mrad, or 50 mrad. Thelight-source field of view and the receiver field of view may haveapproximately equal angular extents. As an example, Θ_(L) and Θ_(R) mayboth be approximately equal to 1 mrad, 2 mrad, or 3 mrad. In someimplementations, the receiver field of view is larger than thelight-source field of view, or the light-source field of view is largerthan the receiver field of view. For example, Θ_(L) may be approximatelyequal to 1.5 mrad, and Θ_(R) may be approximately equal to 3 mrad. Asanother example, Θ_(R) may be approximately L times larger than Θ_(L),where L is any suitable factor, such as for example, 1.1, 1.2, 1.5, 2,3, 5, or 10.

As indicated above, a pixel may represent or correspond to aninstantaneous light-source FOV. As the output beam 532 propagates fromthe light source 122A or 122B, the diameter of the output beam 532 (aswell as the size of the corresponding pixel) may increase according tothe beam divergence Θ_(L). As an example, if the output beam 532 has aΘ_(L) of 2 mrad, then at a distance of 100 m from the lidar system 120Aor 120B, the output beam 532 may have a size or diameter ofapproximately 20 cm, and a corresponding pixel may also have acorresponding size or diameter of approximately 20 cm. At a distance of200 m from the lidar system 120, the output beam 532 and thecorresponding pixel may each have a diameter of approximately 40 cm.

The scanner 11 may be configured to scan the output beam 532 over a5-degree angular range, 20-degree angular range, 30-degree angularrange, 60-degree angular range, or any other suitable angular range. TheFOR of the lidar system 120A or 120B may refer to an area, region, orangular range over which the lidar system 120A or 120B may be configuredto scan or capture distance information. When the lidar system 120 scansthe output beam 532 within a 30-degree scanning range, the lidar system120A or 120B may be referred to as having a 30-degree angular field ofregard. In various implementations, the lidar system 120A or 120B mayhave a FOR of approximately 10°, 20°, 40°, 60°, 120°, or any othersuitable FOR. The FOR also may be referred to as a scan region.

The scanner 11 is configured to scan the output beam 532 horizontally,with each reflective surface of the polygon mirror 12 defining arespective scan line 524, and vertically, where the oscillation of theplanar mirror 14 moves the scan lines 524 upward or downward. The lidarsystem 120 may have a particular FOR along the horizontal direction andanother particular FOR along the vertical direction. For example, thelidar system 120 may have a horizontal FOR of 10° to 120° and a verticalFOR of 2° to 450°.

Referring back to FIGS. 1 and 26A/26B, the controller 130 in oneimplementation generates and dynamically modifies the drive signal forthe motor 64 which oscillates the planar mirror 14. The motor 32 drivingrotation of the polygon mirror 12 may operate in an open-loop mode,without relying on control signals from the controller 130. In thisimplementation, the motor 32 driving the polygon mirror 12 may rotate ata constant speed to generate similar scan lines, while variations in thespeed at which the planar mirror 14 moves relative to the axis ofoscillation can result in some scan lines being farther apart, some scanlines being closer together, etc. Further, the controller 130 can modifythe drive signal for the motor 64 to reposition the entire operationalFOR of the lidar sensor unit 10 within the larger range motion availableto the planar mirror 14. Still further, the controller 130 can modifythe drive signal for the motor 64 to “stretch” the FOR of theoperational FOR of the lidar sensor unit 10 so as to encompass theentire available FOR. In some implementations, the motor 32 drivingrotation of the polygon mirror 12 may operate in a closed-loop mode,where the motor 32 receives a control signal that regulates, stabilizes,or adjusts the rotational speed of the polygon mirror 12. For example,the polygon mirror 12 may be provided with a tab that passes through oneor more stationary photo-interrupters as the polygon mirror 12 rotates.The signals from the photo-interrupters may be sent to the controller130, and the controller 130 may provide a control signal to the motor 32to maintain the rotation speed of the polygon mirror 12 at asubstantially constant value.

In other implementations, however, the controller 130 modifies the drivesignal supplied to the motor 32 to thereby adjust the rotation of thepolygon mirror 12. For example, the controller 130 may slow down therotation of the polygon mirror 12 when the output beam (or a pair ofoutput beams associated with the same eye) traverses the middle of thescan line, so that pixel density near the center of the FOR_(H) ishigher than at the periphery of the FOR_(H).

The controller may modify the drive signal for the motor 32 and/or thedrive signal for the motor 64 dynamically in response to varioustriggering events. In addition to detection of an upward or downwardslope, as discussed in more detail below, examples of suitabletriggering events include detection of a particular object in a certaindirection relative to the vehicle (e.g., if an object is moving quicklyacross the path of the vehicle, the lidar system 120A and 120B maymodify the scan pattern to obtain a higher density rate where the objectis detected to be able to better respond to the potential threat ofcollision), a sound detected at in a certain direction relative to thevehicle, a heat signature detected at in a certain direction relative tothe vehicle, etc.

FIG. 36 depicts an example range 600 within which the lidar system 120can set the operational FOR 602. In the lidar system 120A or 120B, therange of motion for the planar mirror 14 can define a vertical dimensionof the available FOR_(V-AVAIL) (e.g., 90°, 100°, 110°, 120°) thatexceeds the vertical dimension of the operational FOR_(V-OPER) (e.g.,60°). The controller 130 can adjust the drive signal for the motor 64 soas to move the FOR 602 upward or downward relative to the center of theavailable FOR 600.

In some implementations or scenarios, the controller 130 adjusts thedrive signal for the motor 64 so that the FOR_(V-OPER) “stretches” outto cover a larger portion of the FOR_(V-AVAIL). For example, thecontroller 130 may cause the FOR_(V-OPER) to temporarily change from60°×30° to 60°×40° or 60°×30° to 60°×50°. The controller may modify thedrive signal for the motor 64 without modifying the operation of themotor 32 driving the polygon mirror and, as a result, the modificationof the FOR_(V-OPER) from 60°×30° to 60°×40° results in changes indistances between at least some of the scan lines. The controller 130may cause these changes to be uniform or non-uniform (e.g., separate thescan lines near the edges of the FOR_(V) by a larger amount).

Further, the lidar system 120A or 120B can modify the drive signal forthe motor 64 to adjust distances between scan lines. As illustrated inFIG. 37, the distance between the scan lines 524A and 524B is greaterthan the distance between the scan lines 524B and 524C in the exampleFOR 620. The controller 130 generates a drive signal such that theplanar mirror 14 slows down near the middle of the FOR_(V), and speedsup near the fringes of the FOR_(V). The lidar system 120A and 120B canadjust this distance temporarily in view of certain triggeringconditions, in some implementations.

The controller 130 can be configured to modify the one or both drivesignals for the motors 32, 64 on a frame-by-frame basis, with each framecorresponding to a complete scan of the field of regard of the lidarsystem 120A or 120B. In other implementations or scenarios, thecontroller 130 modifies the scan pattern for a certain pre-configuredtime interval (e.g., 10 milliseconds, 100 milliseconds, one second, twoseconds, four seconds). In yet other implementations or scenarios, thecontroller 130 modifies the scan pattern in response to a triggeringevent and restores the default configuration in response to anothertriggering event.

FIG. 38 is a flow diagram of an example method 700 for modifying theFOR. The method 38 can be implemented in the controller 130, forexample, as a set of instructions. The method 700 begins at block 702,where the initial operational FOR for the scanner is selected. Thecenterline of the FOR_(V-OPER) initially can coincide with thecenterline of the FOR_(V-AVAIL). Referring back to FIGS. 1-20, theplanar mirror 14 at block 702 oscillates near the middle of itsavailable range of motion.

At block 704, an upcoming road segment with a grade is detected.Referring to FIG. 39A, for example, a vehicle 750 can detect a downwardslope using the lidar sensor unit 10 and/or other sensors. In thescenario illustrated in FIG. 39B, on the other hand, the vehicle detectsan upward slope. At block 706, the operational FOV is moved upward ordownward. The lidar sensor unit 10 accordingly moves FOR_(V-OPER)downward or upward, respectively, to better “see” along the surface ofthe road. To this end, the controller 130 can adjust the drive signalfor the motor 64. At block 708, the default position of the FOR_(V-OPER)within the FOR_(V-AVAIL) is restored when the vehicle 750 detects thatthe road again is level. The controller 130 again can provide thecorresponding drive signals to the motor 64.

VII. Generating Pixels with Non-Integer Separation in a Lidar SensorUnit

The lidar sensor unit 10 in a two-eye configuration directs output beamson two reflective surfaces of the polygon mirror 12. Moreover, the lidarsensor unit 10 can angularly separate each of the output beams into twooutput beams (see FIG. 25). The two output beams of the same eye mayhave different wavelengths. The lidar sensor unit 10 can use the twooutput beams to scan different pixels in a same scan line during asingle ranging event. The pixels can have non-integer separation such as5.5 pixels or 9.5 pixels, for example. Further, the two eyes of thesensor unit 10 can define an overlap region in which the interleavebetween pixels and/or lines does not correspond to an integer value.Measured angularly, the width of the overlap region may have anysuitable value such as 1, 2, 5, 10, 20, 30, or 40 degrees. The width ofthe overlap region may be determined, at least in part, by the angle ofincidence at which the two output beams which are directed onto the tworeflective surfaces of the polygon mirror 12. Interleaving pixels andinterleaving scan lines in this manner can be implemented separately ortogether in a lidar system.

To detect two pulses within a ranging event for the same eye, the lidarsensor unit 10 can include two detectors for each optical path. FIG. 40is a diagram of a detector array 800 which includes two detector sites802A, 802B, which can be used in the lidar system 120A or 120B, forexample, or another suitable lidar system. Each of the detector sites802A and 802B may include a single detector or a cluster of individualdetectors (APDs, SPADs, etc.) to mitigate potential registration,tolerance, and capacitance issues. The two detector sites 802A and 802Bmay be offset from one another along a direction corresponding to thescanning direction of the light source. The lidar system 120A or 120Bmay use the detector site 802A to scan even pixels and the detector site802B to scan odd pixels. For convenience, detector sites such as thesites 802A and 802B are referred to herein simply as detectors.

In one implementation, a DOE or a free-space splitter disposed in thepath of an output beam may separate pulses by any suitable angle Θ, suchas for example, 1 mrad, 2 mrad, 5 mrad, 10 mrad, 20 mrad, or 50 mrad. Asan example, the splitter may split an emitted pulse into two pulses ofangularly separated light (e.g., a first pulse and a second pulse). Inanother implementation, a pair of collimators may be used to produce anysuitable angle Θ between two pulses. As an example, an emitted pulse maybe split into two pulses by a fiber-optic splitter, and two collimators(e.g., collimators 92A and 94A in FIG. 23) may be arranged to produce anangle of approximately 20 mrad between the two pulses. The scanner 11may scan these pulses of light along a scanning direction across pixelslocated downrange from the lidar system 120A or 120B. The detectors 802Aand 802B in this implementation may be separated by adetector-separation distance along a direction corresponding to thescanning direction of the light pulses. The detector 802A may beconfigured to detect scattered light from the first pulse of light, andthe detector 802B may be configured to detect scattered light from thesecond pulse of light. The controller 130 is configured to determine oneor more distances to one or more targets based at least in part on atime of flight of the first pulse of light or a time of flight of thesecond pulse of light. A respective splitter, DOE, or pair ofcollimators can be used with each of the two eyes of the lidar sensorunit 10.

Referring to FIG. 41, the output beams can be aimed so that the detectorFOV 812A of the detector 802A and the detector FOV 812B of the detector802B initially have little or no overlap (e.g., less than 10% overlap)with the corresponding instantaneous light-source FOVs, or pixel #i or#j. The scanner 11 can be configured so that after the round-trip timecorresponding to the maximum range of the lidar system 120A or 120B haselapsed, the detector FOV 812A has moved so as to coincide with pixel#i, and the detector FOV 812B has moved so as to coincide with pixel #j.In other words, when a scattered pulse of light returns from a target atmaximum operational distance of the lidar system 120, e.g., R_(MAX), theinstantaneous light-source FOV is located in the detector FOV 812A or812B. If a light pulse returns from a location beyond the maximum rangeR_(MAX) (if the target is highly cooperative, for example), the detector802A and 802B generates a weaker signal, which the lidar system 120 canignore, because the FOV 812A or 812B overlaps pixel #i or #j onlypartially.

In one implementation, pulses of light in each output beam are angularlyseparated so as to scan two lines in parallel. Thus, a pulse of light Pcan be split into pulse P′ and P″ to generate pixels in scan lines L_(i)and L_(i+1), so that the planar mirror then can be repositioned to scanlines L_(i+2) and L_(i+3) in the next instance. In anotherimplementation, pulses of light in each output beam are angularly and/orspatially separated and directed toward different sections of a samescan line, so as to produce two pixels within the time of a singleranging event. The two beams in this implementation can be separated bya non-integer number of pixels (e.g., 3.5, 5.5, 7.5, 10.5) so as improvethe resulting pixel quality. More particularly, for a pair of adjacentpixels generated using one beam, another pixel centered at the midpointbetween the pair of pixels can be generated using the other beam, andthe two adjacent pixels can be corrected as necessary using the midpointpixel.

FIG. 42 illustrates an example combined scan pattern 850 according towhich the lidar system 120 can scan the combined FOR of the lidar sensorunit 10. The combined scan pattern 850 includes a scan pattern 852A ofthe first eye of the lidar sensor unit 10 and a scan pattern 852B of thesecond eye of the lidar sensor unit 10. Referring back to FIG. 26B, thescan pattern 852A can correspond to the first eye corresponding to thereceiver 128A, and the scan pattern 852B can correspond to the secondeye corresponding to the receiver 128B. The scan patterns 852A and 852Boverlap in a region 860. In the region 860, the scan lines in the scanpattern 852A are offset relative to scan lines of the scan pattern 852Bby approximately one half of a scan line to yield double pixel densitywithin the overlap region 860. In the forward orientation of the lidarsensor unit 10, the overlap region 860 corresponds to the area directlyahead of the vehicle. The controller 130 or the vehicle controller 372can use the increased pixel density to more accurately identify objectswithin overlap region 860.

FIG. 43 schematically illustrates a technique for scanning pixels withnon-integer separation. In an example scenario 900, pulses of light ineach output beam are directed toward different sections of a same scanline, so as to produce two pixels within the time of a single rangingevent. For example, referring back to FIG. 25, the lidar sensor unit 10during a first ranging event can direct the output beams 110A and 110Bat pixels 1 and 7.5, respectively. In the next ranging event, the lidarsensor unit 10 can direct the output beams 110A and 110B at pixels 2 and8.5, respectively, and during the third ranging event the output beams110A and 110B can be aimed at pixels 3 and 9.5. When the controller 130and/or the vehicle controller 372 processes data from the receiver 128Aof 128B, the values corresponding to pixels with fractional indices(7.5, 8.5, 9.5, etc.) can be used to more accurately determine thevalues of pixels with neighboring integer indices (7, 8, 9, 10, etc.),as illustrated in FIG. 43.

Thus, the lidar sensor unit 10 in this example configurationconcurrently scans pixels with a separation of 6.5 using two outputbeams of the same eye. More generally, the lidar sensor unit 10 canapply non-integer separation of pixels to beams associated with the sameeye or two different eyes. Also, as discussed above, the lidar sensorunit 10 also can apply non-integer separation of pixels to beamsassociated with different eyes.

FIG. 44 is a flow diagram of an example method 950 for generating pixelvalues using output beams with non-integer pixel separation, which canbe implemented in the controller 130 of the lidar system 120A or 120Band/or vehicle controller 372.

At block 952, pixels N, N+1, and N+2 are scanned using a first outputbeam. Pixels N, separated by a non-integer offset, are scanned at block954 to generate pixels N+integer offset+0.5, pixels N+integeroffset+1.5, pixels N+integer offset+2.5, etc. The blocks 954 and 956 areexecuted concurrently. At block 956, the values of pixels are calculatedusing the data generated by scanning the FOR with the first beam and thesecond beam. For example, the value of pixel #27 can be calculated usingthe result of scanning pixel #27 using the first output beam as well asthe result of scanning pixels #26.5 and 27.5 using the second outputbeam. Block 956 can be implemented in the controller 130, for example.

VIII. General Considerations

In some cases, a computing device may be used to implement variousmodules, circuits, systems, methods, or algorithm steps disclosedherein. As an example, all or part of a module, circuit, system, method,or algorithm disclosed herein may be implemented or performed by ageneral-purpose single- or multi-chip processor, a digital signalprocessor (DSP), an ASIC, a FPGA, any other suitable programmable-logicdevice, discrete gate or transistor logic, discrete hardware components,or any suitable combination thereof. A general-purpose processor may bea microprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor may also be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

In particular embodiments, one or more implementations of the subjectmatter described herein may be implemented as one or more computerprograms (e.g., one or more modules of computer-program instructionsencoded or stored on a computer-readable non-transitory storage medium).As an example, the steps of a method or algorithm disclosed herein maybe implemented in a processor-executable software module which mayreside on a computer-readable non-transitory storage medium. Inparticular embodiments, a computer-readable non-transitory storagemedium may include any suitable storage medium that may be used to storeor transfer computer software and that may be accessed by a computersystem. Herein, a computer-readable non-transitory storage medium ormedia may include one or more semiconductor-based or other integratedcircuits (ICs) (such, as for example, field-programmable gate arrays(FPGAs) or application-specific ICs (ASICs)), hard disk drives (HDDs),hybrid hard drives (HHDs), optical discs (e.g., compact discs (CDs),CD-ROM, digital versatile discs (DVDs), blue-ray discs, or laser discs),optical disc drives (ODDs), magneto-optical discs, magneto-opticaldrives, floppy diskettes, floppy disk drives (FDDs), magnetic tapes,flash memories, solid-state drives (SSDs), RAM, RAM-drives, ROM, SECUREDIGITAL cards or drives, any other suitable computer-readablenon-transitory storage media, or any suitable combination of two or moreof these, where appropriate. A computer-readable non-transitory storagemedium may be volatile, non-volatile, or a combination of volatile andnon-volatile, where appropriate.

In some cases, certain features described herein in the context ofseparate implementations may also be combined and implemented in asingle implementation. Conversely, various features that are describedin the context of a single implementation may also be implemented inmultiple implementations separately or in any suitable sub-combination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

While operations may be depicted in the drawings as occurring in aparticular order, this should not be understood as requiring that suchoperations be performed in the particular order shown or in sequentialorder, or that all operations be performed. Further, the drawings mayschematically depict one more example processes or methods in the formof a flow diagram or a sequence diagram. However, other operations thatare not depicted may be incorporated in the example processes or methodsthat are schematically illustrated. For example, one or more additionaloperations may be performed before, after, simultaneously with, orbetween any of the illustrated operations. Moreover, one or moreoperations depicted in a diagram may be repeated, where appropriate.Additionally, operations depicted in a diagram may be performed in anysuitable order. Furthermore, although particular components, devices, orsystems are described herein as carrying out particular operations, anysuitable combination of any suitable components, devices, or systems maybe used to carry out any suitable operation or combination ofoperations. In certain circumstances, multitasking or parallelprocessing operations may be performed. Moreover, the separation ofvarious system components in the implementations described herein shouldnot be understood as requiring such separation in all implementations,and it should be understood that the described program components andsystems may be integrated together in a single software product orpackaged into multiple software products.

Various implementations have been described in connection with theaccompanying drawings. However, it should be understood that the figuresmay not necessarily be drawn to scale. As an example, distances orangles depicted in the figures are illustrative and may not necessarilybear an exact relationship to actual dimensions or layout of the devicesillustrated.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes or illustrates respective embodimentsherein as including particular components, elements, functions,operations, or steps, any of these embodiments may include anycombination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.

The term “or” as used herein is to be interpreted as an inclusive ormeaning any one or any combination, unless expressly indicated otherwiseor indicated otherwise by context. Therefore, herein, the expression “Aor B” means “A, B, or both A and B.” As another example, herein, “A, Bor C” means at least one of the following: A; B; C; A and B; A and C; Band C; A, B and C. An exception to this definition will occur if acombination of elements, devices, steps, or operations is in some wayinherently mutually exclusive.

As used herein, words of approximation such as, without limitation,“approximately, “substantially,” or “about” refer to a condition thatwhen so modified is understood to not necessarily be absolute or perfectbut would be considered close enough to those of ordinary skill in theart to warrant designating the condition as being present. The extent towhich the description may vary will depend on how great a change can beinstituted and still have one of ordinary skill in the art recognize themodified feature as having the required characteristics or capabilitiesof the unmodified feature. In general, but subject to the precedingdiscussion, a numerical value herein that is modified by a word ofapproximation such as “approximately” may vary from the stated value by+0.5%, +1%, +2%, +3%, +4%, +5%, +10%, +12%, or +15%.

As used herein, the terms “first,” “second,” “third,” etc. may be usedas labels for nouns that they precede, and these terms may notnecessarily imply a particular ordering (e.g., a particular spatial,temporal, or logical ordering). As an example, a system may be describedas determining a “first result” and a “second result,” and the terms“first” and “second” may not necessarily imply that the first result isdetermined before the second result.

As used herein, the terms “based on” and “based at least in part on” maybe used to describe or present one or more factors that affect adetermination, and these terms may not exclude additional factors thatmay affect a determination. A determination may be based solely on thosefactors which are presented or may be based at least in part on thosefactors. The phrase “determine A based on B” indicates that B is afactor that affects the determination of A. In some instances, otherfactors may also contribute to the determination of A. In otherinstances, A may be determined based solely on B.

What is claimed is:
 1. A lidar system comprising: one or more lightsources configured to generate a first beam of light and a second beamof light; a scanner configured to scan the first and second beams oflight across a field of regard of the lidar system, the scannercomprising: a rotatable polygon mirror comprising a plurality ofreflective surfaces angularly offset from one another along a peripheryof the polygon mirror, the reflective surfaces configured to reflect thefirst and second beams of light to produce a series of scan lines as thepolygon mirror rotates; and a pivotable scan mirror configured to (i)reflect the first and second beams of light and (ii) pivot to distributethe scan lines across the field of regard; and a receiver configured todetect the first beam of light and the second beam of light scattered byone or more remote targets, wherein the receiver comprises: a firstdetector configured to detect the first beam of scattered light, and asecond detector configured to detect the second beam of scattered light.2. The lidar system of claim 1, wherein the first and second beams oflight are directed to the polygon mirror so that the first and secondbeams of light are both reflected by one reflective surface at a time asthe polygon mirror rotates.
 3. The lidar system of claim 1, wherein thefirst and second beams of light are directed to the polygon mirror sothat, as the polygon mirror rotates, the first and second beams of lightare reflected by different reflective surfaces of the polygon mirror. 4.The lidar system of claim 1, wherein: the one or more light sources arefurther configured to generate a third beam of light and a fourth beamof light; the field of regard is a first field of regard of the lidarsystem, and the scanner is further configured to scan the third andfourth beams of light across a second field of regard of the lidarsystem; and the receiver is a first receiver, and the lidar systemfurther comprises a second receiver configured to detect the third beamof light and the fourth beam of light scattered by one or more otherremote targets, wherein the second receiver comprises: a third detectorconfigured to detect the third beam of scattered light, and a fourthdetector configured to detect the fourth beam of scattered light.
 5. Thelidar system of claim 4, wherein: the first and second beams of lightare directed to the polygon mirror so that the first and second beams oflight are both reflected by one reflective surface at a time as thepolygon mirror rotates; the third and fourth beams of light are directedto the polygon mirror so that the third and fourth beams of light areboth reflected by a different reflective surface as the polygon mirrorrotates, wherein the reflective surfaces are further configured toreflect the third and fourth beams of light to produce another series ofscan lines as the polygon mirror rotates; and the pivotable scan mirroris further configured to (i) reflect the third and fourth beams of lightand (ii) pivot to distribute the another series of scan lines across thesecond field of regard.
 6. The lidar system of claim 4, wherein thefirst field of regard and the second field of regard partially overlapto define an overlap region.
 7. The lidar system of claim 1, wherein thefirst and second beams of light are directed (i) from the one or morelight sources to the polygon mirror and (ii) then from the polygonmirror to the scan mirror, wherein the scan mirror directs the first andsecond beams of light to the field of regard of the lidar system.
 8. Thelidar system of claim 7, wherein the first and second beams of scatteredlight travel in an opposite direction with respect to the first andsecond beams of light, wherein the first and second beams of scatteredlight are directed (i) from the scan mirror to the polygon mirror and(ii) then from the polygon mirror to the receiver.
 9. The lidar systemof claim 1, wherein the lidar system further comprises: a firstfiber-optic cable terminated by a first collimator, wherein the firstcollimator is configured to direct the first beam of light to thescanner; and a second fiber-optic cable terminated by a secondcollimator, wherein the second collimator is configured to direct thesecond beam of light to the scanner.
 10. The lidar system of claim 9,wherein the first and second collimators are configured to launch thefirst and second beams of light, respectively, with a particular spatialoffset or angular offset.
 11. The lidar system of claim 1, wherein: thefirst and second beams of light have a particular spatial or angularoffset; and the first and second beams of scattered light have acorresponding spatial or angular offset.
 12. The lidar system of claim1, wherein the first and second beams of light and the first and secondbeams of scattered light are arranged on a reflective surface of thescan mirror to minimize a surface area associated with the four beams,wherein the first and second beams of scattered light define a largercircle and the first and second beams of light each define a smallercircle arranged adjacent to the larger circle on the reflective surfaceof the scan mirror, wherein a line segment connecting centers of thesmaller circles is displaced relative to a diameter of the largercircle.
 13. The lidar system of claim 1, wherein the scanner isconfigured to scan the first and second beams of light across the fieldof regard synchronously, wherein the first and second beams of light arescanned across the field of regard at approximately equal scanningrates.
 14. The lidar system of claim 1, further comprising a controllerconfigured to modify a drive signal for a motor of the scan mirror toadjust distances between the scan lines.
 15. The lidar system of claim1, wherein a width of a reflective surface of the scan mirror is greaterthan a width of each of the reflective surfaces of the polygon mirror.16. The lidar system of claim 1, further comprising a lens configured tofocus the first and second beams of scattered light onto the first andsecond detectors, respectively.
 17. The lidar system of claim 1, whereinthe first and second detectors are separated by a distance of 0.5 mm to2 mm.
 18. The lidar system of claim 1, wherein the one or more lightsources comprise a laser diode that is current-modulated to produceoptical pulses, wherein the laser diode is followed by one or moreoptical-amplification stages.
 19. The lidar system of claim 1, whereineach of the first and second beams of light comprises pulses of light,wherein each pulse of light has (i) a wavelength between 1400 nm and1600 nm, (ii) a pulse duration between 1 nanosecond and 20 nanoseconds,and (iii) a pulse energy between 0.1 microjoules and 100 microjoules.20. The lidar system of claim 1, wherein: the first beam of lightcomprises a pulse of light, and the first detector includes an avalanchephotodiode (APD) configured to produce an electrical-current pulsecorresponding to scattered light from the pulse of light; and thereceiver further comprises a pulse-detection circuit coupled to the APD,the pulse-detection circuit comprising: a transimpedance amplifier (TIA)configured to receive the electrical-current pulse from the APD andproduce a voltage pulse that corresponds to the receivedelectrical-current pulse; a gain circuit configured to amplify thevoltage pulse; a comparator configured to produce an electrical-edgesignal when the amplified voltage pulse rises above or falls below aparticular threshold voltage; and a time-to-digital converter (TDC)configured to determine an interval of time between emission of thepulse of light and receipt of the electrical-edge signal.
 21. The lidarsystem of claim 1, wherein: the polygon mirror further comprises one ormore tabs configured to pass through a stationary photo-interrupter asthe polygon mirror rotates, wherein the photo-interrupter is configuredto provide data to a controller indicating a rotational speed of thepolygon mirror; and the controller is configured to provide a controlsignal to a motor of the polygon mirror to regulate, stabilize, oradjust the rotational speed of the polygon mirror.
 22. The lidar systemof claim 1, further comprising a baffle or shroud that partiallysurrounds or encloses the polygon mirror.
 23. The lidar system of claim1, wherein the rotatable polygon mirror is a highly balanced rotatablepolygon mirror comprising a block, wherein the highly balanced rotatablepolygon mirror is manufactured by: applying a coarse balancing procedureto the block; and thereafter applying a precise balancing procedure tothe block, comprising (i) imparting rotation to the block and (ii)removing material from the block using high-energy laser pulses.
 24. Thelidar system of claim 1, wherein the rotatable polygon mirror comprisesa block that is made from glass, plastic, polycarbonate, metal, carbonfiber, or ceramic.
 25. The lidar system of claim 1, wherein therotatable polygon mirror comprises a block having edges or corners thatare rounded or chamfered.